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 by the detection component prior to the current rise or fall 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.