A variable valve system varies an operation condition of an engine valve by controlling an angular position of a control shaft in accordance with an operation condition of the engine. The system has an actuating mechanism for actuating the control shaft. The actuating mechanism comprises a mounting member that is connected to one end of the control shaft by means of bolts and has a projection projected axially in an opposite direction of the control shaft; a permanent magnet piece that is mounted on the projection thereby to rotate together with the control shaft; and a sensing device that senses a rotation condition of the permanent magnet piece.