Image forming apparatus

An image forming apparatus comprising:

• a sheet storage section for storing recording sheets;
• a sheet feeder for taking out and conveying a recording sheet from the sheet storage section;
• an image forming section including:
• a plurality of toner image forming devices for forming a monochromatic and color toner image, the toner image forming devices facing an image bearing member;
• the image bearing member for bearing a formed toner image transferred from a toner image forming device;
• and
• a transferring device for transferring the toner image formed on the image bearing member to a recording sheet conveyed by the sheet feeder, wherein among the toner image forming devices in the image forming section, an image forming device for forming a monochromatic image is located at a position having a shortest distance to the transferring device on a moving course of the image bearing member;
• a drive controller for controlling drivings of the sheet feeder and the image forming section;
• an instruction reception section for allowing an operator to selectively instruct forming of a toner image on a recording sheet;
• a mode storing section for storing an image formation preceding mode of making the toner image forming devices start their respective toner image forming operations before the sheet feeder performs conveyance of a recording sheet from the sheet storage section, and a sheet conveyance preceding mode of making the toner image forming devices start their respective image forming operations after the sheet feeder performs conveyance of a recording sheet from the sheet storage section;
• a detecting section for detecting whether an image forming instruction received by said instruction reception section is an instruction for forming a monochromatic image or a color image;
• a mode determining section which determines to set the image formation preceding mode when said detecting section detects a color image forming instruction where a recording sheet arrives at the transferring position in advance if the toner image formation and the sheet feeder are started at the same time so as to reduce a waiting time of a recording sheet before the transferring position, thereby shortening the time required for transferring a toner image, while determining to set the sheet conveyance preceding mode when said detecting section detects a monochrome image forming instruction where the toner image arrives at the transferring position in advance if the toner image formation and the sheet feeder are started at the same time so as to prevent a delay in arrival of the recording sheet to the transferring position, thereby reducing waste toner image;
• and
• a registration device provided in a sheet conveying passage on upstream side in a recording sheet conveying direction from the transferring device and adapted for continuing or suspending a conveyance of a recording sheet conveyed by the sheet feeder;
• wherein the drive controller controls the drivings of the sheet feeder and the image forming section according to the mode determined by the mode determining section and controls driving of the registration device to adjust an arrival timing of the recording sheet conveyed by the sheet feeder to the transferring position according to the mode determined by the mode determining section.