To provide an engine revolution detector having a small number of part items and excellent resistance to noises.

A rotational angle detector S for detecting the rotational angle of a camshaft 3 is provided with housings 5 and 6 made of conductive materials and provided in the end wall of a cylinder head 1, detecting rotors 14 and 15 provided in the shaft end of the camshaft 3 and detecting elements 24 arranged oppositely to the detecting rotors 14 and 15. An electronic control units C for controlling the running condition of the engine are contained in the housings 5 and 6 and the processing circuit of the rotational angle detector S is assembled in the circuit board 20 of each of the electronic control unit C. By providing the common housings 5 and 6 in the rotational angle detector S and the electronic control unit C, the number of part items is reduced, a harness for connecting these is made unnecessary and thus resistance to noises is improved.