A speed calculation device is provided. The generation component generates a plurality of pulse signals with different phases in accordance with rotation of a rotating body. The detection component detects rises and falls of respective pulses of the plurality of pulse signals generated by the generation component. The duration calculation component, each time a rise or fall is detected by the detection component, calculates a total duration of a pre-specified number of durations representing detection intervals of rises or falls detected prior to the rise or fall currently detected by the detection component. The speed calculation component calculates a speed relating to rotation of the rotating body on the basis of the total duration and a rotation angle of the rotating body that corresponds to one pulse of the pulse signals.