To facilitate suitable diagnosis of existence/nonexistence of torque abnormality.

Teeth part 22a disposed to a signal rotor 22 of a crankshaft 20 is detected by a crank angle sensor to detect behavior of the crankshaft 20. Instantaneous torque by combustion of fuel is calculated from a difference between a time T30(n) required for rotation of a rotational angle of 30CA from, particularly, a compression top dead center and a time T30(n-2) required for rotation of a rotational angle of BTDC60-BTDC30CA before the time T30(n), and an average revolution speed of the moment. At this time, from the difference between the time T30(n) and the time T30(n-2), a quantity caused by an angular error of the tooth parts 22a defining the rotational angle is compensated.