Patent ID: 8498558

Claim:
An image forming apparatus comprising: a latent image forming unit that emits light in accordance with image data on receiving input of the image data, and that scans and exposes an image carrier with the light, to form a latent image on the image carrier; a transfer body on which a toner image is transferred and a reference index is formed, the toner image being formed by developing the latent image on the image carrier, the reference index serving as a reference for setting an output start time point from which the image data is outputted to the latent image forming unit; a detecting unit that is arranged so as to face the reference index formed on the transfer body, and that outputs a detection signal changing in accordance with passing of the reference index; a measuring unit that measures change duration time from a first change occurring in the detection signal outputted from the detecting unit to a second change occurring after the first change; and a controller that controls, by using the detection signal outputted from the detecting unit, the output start time point of the image data to the latent image forming unit, wherein the controller starts, concurrently with the first change occurring in the detection signal, a first period having a first time length during which changes occurring in the detection signal are ignored, starts, after an elapsing of the first period, a second period having a second time length, regards an initial change of the detection signal subsequent to the start of the second period as the reference of the output start time point of the image data, if the change duration time measured by the measuring unit is longer than a predetermined time period, and ignores changes of the detection signal after the initial change of the detection signal subsequent to the start of the second period occurs.