An image forming apparatus including a carriage including image forming units, the carriage driven reciprocally in a main scanning direction; a conveyance unit to convey a sheet of recording media to a position where the image forming units perform image formation; a first detector provided to the carriage, the first detector including a light emitting part and a light receiving part to periodically detect a surface of the sheet; a calculation unit to calculate a relative amount of movement between the sheet and the image forming units by comparing patterns periodically detected by the first detector; and a control unit to control a timing to perform image formation by the image forming units and an amount of conveyance of the sheet conveyed by the conveyance unit based on a result calculated by the calculation unit.