Image reading apparatus equipped with original-size-detection function and image forming apparatus equipped with image reading apparatus

An image forming apparatus comprising:

• an image reading apparatus comprising:
• an opening-closing detection unit configured to detect an opening/closing state of a pressure plate that presses an original to a platen;
• a light source that irradiates the original placed on the platen with light;
• a line sensor configured to receive light reflected by the original at a reading position, and to output image signals;
• a timing signal generating circuit configured to output a line periodic signal to the line sensor and to output a lighting control signal that is supplied to the light source in synchronization with the line periodic signal supplied to the line sensor;
• a controller configured to detect the length of the original in a predetermined direction that is perpendicular to a moving direction of the reading position based on the image signals output from the line sensor,
• wherein the timing signal generating circuit is configured to output a first line periodic signal having a period longer than a period of a second line periodic signal at a time of reading an original image to the line sensor, and to output a first lighting control signal having a first duty ratio smaller than a second duty ratio at the time of reading the original image to the light source, in accordance with the opening-closing detection unit detecting the closing state, from the opening state, corresponding to a predetermined angle, and
• wherein the first duty ratio relates to a ratio of a period during which the light source is lit during the period of the first line period signal;
• and
• a printer configured to print the image read by the image reading apparatus.