An electric motor, in particular a separately excited synchronous motor, has a rotor shaft with at least one slip ring and at least one electrically conductive contact element, in particular a carbon brush, which bears against the slip ring and is accommodated in a channel-like guide formed in a housing and extending radially with respect to the rotor shaft and which carbon brush is radially tensioned against the slip ring by means of a spring element, wherein a roller is provided which is tensioned laterally against the contact element via a further spring element and via which the contact element is tensioned against a wall of the guide.