Wave forces acting on circular, square and diamond cylinders and a flat plate horizontally submerged with their axises parallel to the regular wave crests are experimentally investigated. A rapid reduction of the wave forces acting on the cylinders at low K_c number region is found to be caused by a circulating flow round the cylinder which is created by viscous wake. Flow visualization demonstrates that much larger separated vortices than those in plane oscillatory flow are created in regular waves. It is found that the vortex shedding patterns in regular wave is similar to those in plane oscillatory flow at the corresponding K_c number if a new K_c , number in terms of the circumference of the orbital motion of a fluid particle in waves instead of the diameter is defined.