Abstract: With a device for heating parts 8 made of a microwave absorbing plastic and having a microwave generator 1 that generates microwaves of a certain wavelength, an antenna 4 to which the microwaves are conducted, having at least one free end 5 and a device 6 which surrounds the antenna 4, it is proposed that the device for shielding 6 be designed with a tubular shape, so that the device 6 has an inside diameter smaller than half the wavelength, projects beyond the free end 5 of the antenna and has an opening 7 in its end face. With this device it is possible to achieve a spatially limited and nevertheless homogeneous heating of parts 8. Furthermore a method of heating or welding, shaping or crosslinking parts made of a microwave absorbing plastic using this device is also proposed.