PURPOSE: To smooth timing of jam handling by detecting an abnormal condition in conveyance of a sheet on the basis of a comparison result between an expected passing time of a sheet and an actual normal time when an inputted sheet size corresponds to a size of the previously conveyed sheet or when they do not correspond to each other.

CONSTITUTION: When paper loaded in a paper cassette 2 is fed by means of a paper feeding roller 1 and a paper tip is detected by means of a TOP sensor 3, a timer for measuring paper length is actuated. By means of the timer, an expected passing time for an inputted sheet whose size corresponds to a size of the previously conveyed sheet is compared with a detected actual passing time, and on the basis of this result, abnormal conveyance of a sheet is determine. When sheet sizes do not correspond to each other, an expected passing time for a sheet whose size corresponds to the maximum sheet size is compared with a detected actual passing time, and on the basis of this result, abnormal conveyance of a sheet is determined. Therefore, a jam can be handled smoothly.