A variable valve actuation mechanism of an engine having a reference angle detecting device, the reference angle detecting device comprising: a control shaft connected to a controlled object in order to control an angle of the controlled object, wherein the control shaft is configured to change a lift characteristic of an intake valve or an exhaust valve of the engine according to the rotation angle of the control shaft; a worm wheel connected to the control shaft so as to cause the control shaft to rotate about an axial center thereof; a worm gear that meshes with the worm wheel; an electric motor for rotating the worm gear; a controller that controls the electric motor; a stopper (80, 180) disposed on a motion track of the worm wheel in order to restrict a rotatable range of the control shaft; and an angle sensor capable of detecting a rotation angle of the control shaft, wherein the stopper (80, 180) includes a spring member (84, 182) that is elastically deformable in an operation direction of the worm wheel, and the controller drives the electric motor to operate so that the worm wheel comes to face the stopper (80, 180), characterized in that the controller stores as a reference angle a rotation angle at a time point when a change rate of the rotation angle detected by the angle sensor during drive of the electric motor changes from a value equal to or higher than a predetermined threshold to a value less than the threshold, the controller has a normal control mode in which the electric motor is driven to operate in order to control the angle of the controlled object, and a reference angle detection mode in which the electric motor is driven to operate in order to detect the reference angle; and the controller controls the electric motor so that driving power of the electric motor in the reference angle detection mode is smaller than driving power of the electric motor in the normal control mode. a control shaft connected to a controlled object in order to control an angle of the controlled object, wherein the control shaft is configured to change a lift characteristic of an intake valve or an exhaust valve of the engine according to the rotation angle of the control shaft; a worm wheel connected to the control shaft so as to cause the control shaft to rotate about an axial center thereof; a worm gear that meshes with the worm wheel; an electric motor for rotating the worm gear; a controller that controls the electric motor; a stopper (80, 180) disposed on a motion track of the worm wheel in order to restrict a rotatable range of the control shaft; and an angle sensor capable of detecting a rotation angle of the control shaft, wherein the stopper (80, 180) includes a spring member (84, 182) that is elastically deformable in an operation direction of the worm wheel, and the controller drives the electric motor to operate so that the worm wheel comes to face the stopper (80, 180), characterized in that the controller stores as a reference angle a rotation angle at a time point when a change rate of the rotation angle detected by the angle sensor during drive of the electric motor changes from a value equal to or higher than a predetermined threshold to a value less than the threshold, the controller has a normal control mode in which the electric motor is driven to operate in order to control the angle of the controlled object, and a reference angle detection mode in which the electric motor is driven to operate in order to detect the reference angle; and the controller controls the electric motor so that driving power of the electric motor in the reference angle detection mode is smaller than driving power of the electric motor in the normal control mode.