Image forming apparatus

An image forming apparatus comprising:

• a black image forming portion including an image bearing member and a black developing device including a black toner;
• a color image forming portion which includes a yellow developing device including a yellow toner, a magenta developing device including a magenta toner and a cyan developing device including a cyan toner;
• an intermediary transfer member capable of carrying a toner image formed at said black image forming portion and a toner image formed at said color image forming portion;
• a transfer portion configured to transfer the toner image from said intermediary transfer member onto a recording material;
• an executing portion capable of executing an operation in a color mode in which a color image is formed on the recording material by using said color image forming portion and said black image forming portion and an operation in a monochromatic mode in which a monochromatic image is formed on the recording material by using only said black image forming portion;
• and
• a common voltage source configured to apply a voltage to said black developing device, said yellow developing device, said magenta developing device end said cyan developing device,
• wherein said executing portion is capable of forming the monochromatic image in the operation in the monochromatic mode under application of the voltage to said black developing device, the voltage being applied under a voltage condition such that a line width is broader than a line width under a voltage condition inputted to said black developing device when the operation in the color mode is executed.