Wave forces exerted on circular cylinders in regular waves are investigated. The circular cylinders are fixed horizontally below the water surface. Experimental results are compared with values calculated by linear theory and the other data obtained differently. Main conclusions obtained are as follows : 1) In case of small period parameters, inertia coefficients obtained by experiments show good agreement with theoretical values calculated by linear theory. But for large period parameters, the experimental values are much smaller than the theoretical ones. 2) For large period parameters, drag coefficients derived in the present investigation approximately coincide with those obtained in experiments on hydrodynamic forces acting on circular cylinders in oscillatory flow. But there is much difference between them in case of not so large period parameters.