A sheet processing apparatus according to an aspect of the invention can process a first-size sheet having a first length and a second-size sheet having a second length smaller than the first length. The sheet processing apparatus includes an intermediate stacking portion on which the sheets are stacked; a stapler which performs a stapling process to the sheets; a second alignment reference wall and a first jogger which align the sheets with a stapling process position; and a second jogger which is moved toward the second alignment reference wall and first jogger. Irrespective of a sheet size, the second jogger is moved toward the second alignment reference wall and first jogger by an alignment distance necessary to align the second-size sheet with a stapling process position, which allows the stapler to staple the sheets with at least one of two staple legs.