Patent ID: 8838011

Claim:
An image forming apparatus comprising: an image forming unit for forming an unfixed image on a sheet; a fixing unit for fixing the unfixed image onto the sheet, said fixing unit including rotatable members for forming a fixing nip portion that pinches and conveys the sheet and a heater for heating the unfixed image; a sheet size detecting unit for detecting a size of the sheet, the sheet size detecting unit comprising: a first arm moved by a moving sheet contacting therewith; a second arm moved by the moving sheet contacting therewith, said second arm being disposed at a location differing from that of said first arm in a direction orthogonal to the movement direction of the sheet; a sensor; and an actuator acting on said sensor, wherein said actuator is not moved when only one of said first arm and said second arm is moved by the contact of the sheet, and is moved when both of said first arm and said second arm are moved by the contact of the sheet, wherein the output level of said sensor when only one of said first arm and said second arm has been moved is the same as the output level thereof when neither of said first arm and said second arm is moved, and the output level of said sensor when both of said first arm and said second arm have been moved differs from the output level thereof when neither of said first arm and said second arm is moved, and wherein said first arm has a first regulating portion for regulating the movement of said actuator, said second arm has a second regulating portion for regulating the movement of said actuator, and said actuator is moved only when both said first regulating portion and said second regulating portion are moved by the contact of said first arm and said second arm with the sheet.