An image forming apparatus picks up each one of sheets stacked in a tray, allows a detecting sensor to detect whether a mark indicating a reusable sheet is assigned to the picked-up sheet, and cumulates the sheet in which the mark is not detected by the detecting sensor in a cumulative unit. The image forming apparatus erases a color of an image forming material by heating the sheet of which the mark is detected by the detecting sensor and receives the sheet of which the image forming material is erased in a sheet cassette. The image forming apparatus forms an image with the image forming material erasable by applying heat to the sheet received in the sheet cassette.