Velocity calculation device, image forming apparatus, and computer readable storage medium

A velocity calculation device comprising:

• a rotation body provided with a plurality of detected portions disposed along a rotation direction at predetermined rotation angle intervals;
• a plurality of generating sections that each respectively generate a pulse signal according to passing of each of the plurality of detected portions accompanying rotation of the rotation body;
• a detection section that detects as individual periods, based on each of the pulse signals generated by the plurality of generating sections, periods of each of the pulse signals of the plurality of generating sections;
• a computation section that, using as a reference period at each of a plurality of predetermined points in time the individual period detected most recently by the detection section for one or other of the plurality of generating sections, computes for each of the reference periods an average value of the reference period and one or more individual periods for other generating sections of the plurality of generating sections, detected separately prior to detecting the respective reference period for pulse signals nearest to the reference period;
• and
• a calculation section that calculates a velocity related to rotation of the rotation body based on the plurality of average values computed by the computation section, the number of individual generating sections, and the predetermined rotation angle.