To provide a compulsive opening and closing valve device capable of achieving miniaturization of a cylinder head by allowing alignment errors of a valve system to be reliably and easily absorbed and allowing clearance to be reliably and easily adjusted.

In an SOHC rocker arm type compulsive opening and closing valve device, a roller follower 24 is adopted, a cam follower arm and a valve lift arm are integrally formed, an engagement position adjusting mechanism of a retainer having flange parts at upper and lower parts of a cylindrical part fixed to a valve shaft has a small and lightweight structure, and a valve 31 is compulsively opened and closed. Accordingly, a valve opening angle can be narrowed while improving output, a setting degree of freedom of an overlap angle can be increased, and angle errors of the flange parts are easily absorbed. A cam, a rocker arm, an ignition plug hole 61 or an injector hole, and an intake port 1IN are arranged in a space or the like obtained by abolishing a valve spring 39 or reducing the size thereof, and the size of a cylinder head 1 and an angle of the intake port with respect to a cylinder axis are reduced to improve intake efficiency and a tumble flow.