Image forming apparatus

An image forming apparatus comprising:

• a first scanned medium configured to be scanned with a first optical signal based on first image data;
• a second scanned medium configured to be scanned with a second optical signal based on second image data;
• a rotary polygon mirror configured to deflect the first optical signal and the second optical signal;
• a synchronization detection signal generation circuit configured to generate a synchronization detection signal representing a first scanning start time to start scanning the first scanned medium;
• and
• at least one pseudo synchronization detection signal generation circuit configured to generate a pseudo synchronization detection signal with the synchronization detection signal, the pseudo synchronization detection signal representing a second scanning start time to start scanning the second scanned medium,
• the at least one pseudo synchronization detection signal generation circuit being configured to
• based on a previously calculated period of the synchronization detection signal and a period of the synchronization detection signal counted on a particular surface of the rotary polygon mirror, generate a particular value for generating the pseudo synchronization detection signal, and
• based on the generated particular value, starts generating the pseudo synchronization detection signal at a time at which the synchronization detection signal is enabled.