Image forming apparatus and image forming method

An image forming apparatus comprising:

• a light scanning portion that lights a plurality of beams, and scans a surface to be scanned of an image carrier to form an electrostatic latent image;
• a detection portion that detects at least one beam lighted by the light scanning portion;
• an abnormality detection portion that transmits data to the light scanning portion via a transmission-line, causes the light scanning portion to light a beam, and detects abnormality of the transmission-line based on the beam detected by the detection portion;
• and
• a setting portion that sets a number of beams to be lighted by the light scanning portion in the case of the formation of the electrostatic latent image so that an amount of light of the beam detected by the detection portion in the case of abnormality detection of the transmission-line by the abnormality detection portion is equal to or more than a minimum amount of light of the beam detected by the detection portion in the case of the formation of the electrostatic latent image.