An image forming apparatus includes a sheet feed cassette. The sheet feed cassette has a cylinder lock having a cylinder, and a turning unit coupled to the cylinder to be rotatable integrally with the cylinder. A switch switching part of the turning unit is configured to switch a power switch such that the power switch is in an ON state when an inner cylinder of the cylinder lock is at an unlocked position, and the power switch is in an OFF state when the inner cylinder is at a locked position. A cassette locking part of the turning unit is configured to place a sheet feed cassette of a standard sheet feeder in an unlocked state when the inner cylinder of the cylinder lock is at the unlocked position and place the sheet feed cassette in a locked state when the inner cylinder is at the locked position.