A press machine slide stroke adjusting apparatus comprises an eccentric sleeve connected to a slide and fitted over a circular eccentric portion of a crank shaft, first teeth provided on the eccentric sleeve and concentric to the circular eccentric portion, a main gear disposed on the crank shaft in coaxial relationship therewith, and second teeth meshing with the first teeth and provided on main gear coaxially with the crank shaft. The crank shaft is disconnected and connected from and to the main gear by coupling. A hydraulic actuator disengages the crank shaft from the main gear. The rotation of the crank shaft disconnected from the main gear is prevented by engagement of a pin and an engaging hole in an engaging block. Under such conditions, the eccentric sleeve is turned relative to the circular eccentric portion to adjust a vertical stroke of the slide.