not shown via a crank sprocket and a timing chain the rotor 20 is unitary secured to the camshaft 10 with an assembling bolt not shown the rotor 20 includes four vane grooves 21 a receiving groove 22 four advance angle passages i e serving as a first hydraulic passage 23 extended in a radial direction and four retarded angle passages i e serving as a second hydraulic passage 24 extended in a radial direction four vanes 70 70 70 a 70 b are provided in respective vane grooves 21 to be movable in the radial direction a leaf spring 73 shown in fig5 6 is provided between a bottom portion of the vane groove 21 and a bottom surface of the vane 70 thus as shown in fig5 6 the vane 70 is always biased outwardly by the leaf spring 73 while sliding on a sliding surface of the housing 30 the receiving groove 22 is provided with a lock key 80 whose head portion enters the receiving groove 22 by a predetermined amount when relative positions between the camshaft 10 and the rotor 20 and the housing 30 are synchronized at a predetermined phase i e a most retarded angle position the receiving groove 22 is in communication with one of the advance angle passages 23 the housing 30 is rotatably assembled relative to an external periphery of the rotor 20 within a predetermined angle range the timing sprocket 31 is integrally formed on the external periphery of the housing 30 four convex portions 33 are formed on an internal periphery of the housing 30 in a peripheral direction internal peripheral surfaces of the convex portions.