Provided is a sheet processing apparatus, including: a regulation portion configured to contact with an end edge of a sheet to be conveyed and to regulate a position of the sheet; a position adjustment portion configured to perform position adjustment on a sheet in a direction along an end edge of the sheet of which the end edge is in contact with the regulation portion; a folding portion configured to perform folding processing on a sheet which has been regulated by the regulation portion; and a control portion configured to execute: a first mode of causing the folding portion to perform the folding processing on a sheet which has been regulated by the regulation portion, without causing the position adjustment portion to perform the position adjustment on the sheet; and a second mode of causing the position adjustment portion to perform the position adjustment with respect to the regulated sheet.