Sheet size detecting apparatus

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 includes 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,
• wherein 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 crossing the movement direction of the sheet;
• and
• a sensor;
• wherein said first arm has a first actuator portion for acting directly on said sensor, and said second arm has a second actuator portion for acting directly on said sensor, said first arm and said second arm being independently movable with each other,
• 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.