A device (20) for bonding or welding a membrane, including an undercarriage (30) for supporting the device on the membrane at least at one contact point, which is formed by a pressing element (40) for pressing the membrane onto a metal plate to be bonded or welded thereto, and at least at two further contact points, which are formed by castors (31, 32). A frame (42) extends upwards from the undercarriage (30), wherein the device (20) can be manoeuvred using the frame. The pressing element (40) includes a heating device (46), which is designed as an induction coil, by which the metal plate, which is provided with an adhesive or weldable coating, can be heated. An induction generator and a control and cooling device thereof are mounted in or on a housing (50), which is fixed to the frame (42) at a distance (A) above the undercarriage (30). The device (20), which is formed as one part, can be tilted for moving around a castor axis (28) and can then be lowered via the metal plate onto the membrane.