Abstract: An Antirotation device for an element being moveable back and forth along an axis, particularly a periodically actuable tappet for a valve train or a pump, comprises following features: The device is substantially mushroom-shaped consisting of one trunk section and one head section, the trunk section is circular-cylindrical-like and designed to be arranged in a circular hole or cavity of said element, particularly of a hollow circular-cylindrical part of said element, and the head section is between a longitudinal cut-off of a circular-like cylinder and a cut-off of a spherical and designed to slide in a guide of a bore surrounding said element.