A boarding and/or access aid for vehicles with passenger carrying service has a frame with two parallel side parts and an end profile connecting the latter, a step plate supported in the side parts so that it can be extended and retracted, and a drive for the step plate, supported on the frame, arranged between the two side parts and comprising a drive motor. The drive has a drive element, a chain or a belt, guided over at least one deflection roller, and a drive roller arranged in the area of the end profile, coupled to the drive motor, having a larger diameter than the deflection roller, and arranged in a inner space surrounded by the frame. A pressure roller acting from the outside on an upper belt side of the drive element is associated with the drive roller so that the upper belt strand is arranged between it and the deflection roller parallel to the movement path but underneath the latter.