Apparatus for and method of forming image using oscillation mirror

An image forming apparatus comprising:

• a latent image carrier that has an effective image region having a predetermined width along a main scanning direction;
• a latent image forming section that, using a deflection mirror surface that oscillates, makes a light beam emitted from a light source scan a second scanning area that includes and is wider than a first scanning area corresponding to the effective image region along the main scanning direction, and forms a latent image in the effective image region on the latent image carrier with the light beam scanned;
• a light amount adjuster that adjusts an amount of the light beam emitted from the light source when the light beam moves outside the first scanning area but within the second scanning area;
• and
• a detector that detects the light beam scanned outside the first scanning area but within the second scanning area, wherein
• the detector outputs a first detection signal when the light beam scanned that is traveling away from the effective image region moves past the detector,
• the detector outputs a second detection signal after the first detection signal when the light beam scanned that is traveling toward the effective image region moves past the detector, and
• the light amount adjuster starts adjusting the amount of the light beam in response to the first detection signal.