A sensing device for detecting, based on a pulse signal output from an encoder provided to a rotary body, a speed of the rotary body, a movement direction of the rotary body, and an abnormal state of the pulse signal, the sensing device comprising: an encoder comprising three sensors (11, 12, 13) provided to the rotary body, three sensors (11, 12, 13) outputting pulse signals which repeat ON and OFF every 180 electrical degrees, as three pulse signals (A, B, C) shifted by 120 electrical degrees; a speed signal generation section (20, 22) for receiving the three pulse signals (A, B, C), generating a combined signal as an exclusive OR combination of the three pulse signals, as a speed signal of the rotary body; a direction detection section (40, 42) for receiving the three pulse signals (A, B, C), selecting two of the received three pulse signals, and generating a movement direction signal of the rotary body based on state transitions of the selected two of the received three pulse signals; and a dynamic error diagnosis section for receiving the three pulse signals (A, B, C), and generating a second encoder error state signal by specifying, through monitoring of current three-bit states (Sn) of the received three pulse signals and state transitions between previous three-bit states (S(n-1),...) to reach the current states, one of the three pulse signals as a pulse signal in which it is recognized that there is a transition error, further comprising a static error diagnosis section for receiving the three pulse signals (A, B, C), monitoring the state of the received three pulse signals, determining, when having detected the case when the three pulse signals are all in an ON state and the case when the three pulse signals are all in an OFF state, that an error state is caused in which it is recognized that there is a transition error in one of the three pulse signals, and generating an encoder error state signal. an encoder comprising three sensors (11, 12, 13) provided to the rotary body, three sensors (11, 12, 13) outputting pulse signals which repeat ON and OFF every 180 electrical degrees, as three pulse signals (A, B, C) shifted by 120 electrical degrees; a speed signal generation section (20, 22) for receiving the three pulse signals (A, B, C), generating a combined signal as an exclusive OR combination of the three pulse signals, as a speed signal of the rotary body; a direction detection section (40, 42) for receiving the three pulse signals (A, B, C), selecting two of the received three pulse signals, and generating a movement direction signal of the rotary body based on state transitions of the selected two of the received three pulse signals; and a dynamic error diagnosis section for receiving the three pulse signals (A, B, C), and generating a second encoder error state signal by specifying, through monitoring of current three-bit states (Sn) of the received three pulse signals and state transitions between previous three-bit states (S(n-1),...) to reach the current states, one of the three pulse signals as a pulse signal in which it is recognized that there is a transition error, further comprising a static error diagnosis section for receiving the three pulse signals (A, B, C), monitoring the state of the received three pulse signals, determining, when having detected the case when the three pulse signals are all in an ON state and the case when the three pulse signals are all in an OFF state, that an error state is caused in which it is recognized that there is a transition error in one of the three pulse signals, and generating an encoder error state signal.