A crank angular velocity measuring device that is adapted to measure a crank angular velocity of an engine, the crank angular velocity measuring device comprising: an AC rotary electric machine that is configured to rotate synchronously with a crankshaft, the AC rotary electric machine being provided with a rotor in which permanent magnets of an S pole and permanent magnets of an N pole are alternately and circumferentially arranged at equal intervals, and first, second, and third magnetic sensors (61a, 61b, 61c) arranged in this order along a direction aligned with the circumference of the rotor to detect a corresponding magnetization boundary (Bn) of the same polarization change between the permanent magnets; a clocking means (51a, 5 1b, and 51c) that is adapted to count repeatedly for each corresponding magnetization boundary a first elapsed time (Δt1) from detection of the corresponding magnetization boundary by a first magnetic sensor to detection of the corresponding magnetization boundary by a second magnetic sensor, a second elapsed time (Δt2) from detection of the corresponding magnetization boundary by the second magnetic sensor to detection of the corresponding magnetization boundary by a third magnetic sensor, and a third elapsed time (Δt3) from detection of the corresponding magnetization boundary by the third magnetic sensor to detection of the next corresponding magnetization boundary by the first magnetic sensor; and a moving average calculating means that is configured to calculate repeatedly the crank angular velocity based on a moving average of the first, second, and third elapsed times, wherein an interval A is between the first and second magnetic sensors (61a and 61b) and between the second and third magnetic sensors (61b and 61c), an interval B between the corresponding magnetization boundary (Bn) and the next corresponding magnetization boundary (Bn+1) is longer than 2A, a measured distance in the first elapsed time (Δt1) is A, a measured distance in the second elapsed time (Δt2) is A, and a measured distance in the third elapsed time (Δt3) is B - 2A, and whereby the interval B is 60°. an AC rotary electric machine that is configured to rotate synchronously with a crankshaft, the AC rotary electric machine being provided with a rotor in which permanent magnets of an S pole and permanent magnets of an N pole are alternately and circumferentially arranged at equal intervals, and first, second, and third magnetic sensors (61a, 61b, 61c) arranged in this order along a direction aligned with the circumference of the rotor to detect a corresponding magnetization boundary (Bn) of the same polarization change between the permanent magnets; a clocking means (51a, 5 1b, and 51c) that is adapted to count repeatedly for each corresponding magnetization boundary a first elapsed time (Δt1) from detection of the corresponding magnetization boundary by a first magnetic sensor to detection of the corresponding magnetization boundary by a second magnetic sensor, a second elapsed time (Δt2) from detection of the corresponding magnetization boundary by the second magnetic sensor to detection of the corresponding magnetization boundary by a third magnetic sensor, and a third elapsed time (Δt3) from detection of the corresponding magnetization boundary by the third magnetic sensor to detection of the next corresponding magnetization boundary by the first magnetic sensor; and a moving average calculating means that is configured to calculate repeatedly the crank angular velocity based on a moving average of the first, second, and third elapsed times, wherein an interval A is between the first and second magnetic sensors (61a and 61b) and between the second and third magnetic sensors (61b and 61c), an interval B between the corresponding magnetization boundary (Bn) and the next corresponding magnetization boundary (Bn+1) is longer than 2A, a measured distance in the first elapsed time (Δt1) is A, a measured distance in the second elapsed time (Δt2) is A, and a measured distance in the third elapsed time (Δt3) is B - 2A, and whereby the interval B is 60°.