Variable valve timing device and assembly method of variable valve timing device

A variable valve timing device comprising:

• a case for rotating integrally with a crankshaft of an engine;
• a rotor housed in the case, to be rotated integrally with a camshaft of the engine by fastening the rotor coaxially to the camshaft with a center bolt;
• and
• at least one torque receiving part provided around an axis of the rotor on an opposite side of the rotor to the camshaft, and having a flat surface intersecting a rotation direction of the rotor, wherein
• the at least one torque receiving part is a groove whose side wall includes the flat surface,
• the rotor has a recess in a center of a hub,
• the groove is provided on a bottom surface of the recess,
• the groove has an inner wall on a radially inner side of the groove and an inner wall on a radially outer side of the groove, and the inner walls face each other across the groove and intersect the side wall, and
• the inner wall on the radially outer side is continuous with and flush with an inner wall of the recess.