An image forming apparatus, in which a trailing edge regulation portion is moved to a position according to a sheet contained in a cassette body to regulate a position of the sheet. A positioning lever is swingably provided to the trailing edge regulation portion to be engaged with a rack tooth row provided on the cassette body. The trailing edge regulation portion is held by the positioning lever at a regulation position according to the sheet. When a force in a sliding direction is applied to the trailing edge regulation portion, the trailing edge regulation portion is moved to be brought into pressure contact with the positioning lever, thereby regulating movement in an engagement releasing direction of the positioning lever engaged with the rack tooth row.