An image forming apparatus includes: a cassette including a first and a second sheet storage areas, arranged side by side, each on which a sheet having a predetermined size is placeable; a sheet feeder configured to feed the sheet from the first area to an image forming portion; a first sheet sensor; a second sheet sensor; a movement member configured to move the sheet from the second area to the first area when no sheet placed on the first area is detected by the first sheet sensor and the sheet placed on the second area is detected by the second sheet sensor; and an annunciator configured to annunciate that a sheet having a size different from the predetermined size is placed on the cassette when the first sheet sensor does not detect the sheet after a completion of a movement of the sheet.