An image forming apparatus includes a stack portion, a regulation portion, a detection unit, and a control unit. The regulation portion regulates a position of an edge of recording material stacked on the stack portion. The detection unit detects the position of the edge of the stacked and regulated recording material, and outputs a detection signal per the recording material edge detected position. Where the position of the recording material edge is detected, the control unit obtains a first width of the recording material stacked on the stack portion, calculates a second width of the recording material based on the detection signal output from the detection unit, and obtains a third width of the recording material by correcting a width of the recording material based on difference information between the second width of the recording material and the first width of the recording material.