In a case where crowning is provided on a contact surface of a tappet roller by the combination of, for example, two circular arcs, a logarithmic crowning is determined in which an edge load does not occur in the bearing pressure even if its inclination with respect to the cam is 5/1,000 or thereabouts, and a crowning profile is set between two logarithmic crownings. In addition, the crowning profile is defined so as to be present between the logarithmic crownings in a case where the axial position x with the center in the direction of a bus set as an origin is at a position 0.85-fold and at a position 1.0-fold the half L.sub.e of the effective contact length, respectively.