A method of manufacturing a medical heater that includes arranging, on an electrically isolated substrate, (i) a heating element configured to generate heat based on a supply of electric current to the heating element, (ii) a metal film electrically connected to the heating element, and (iii) a wiring member bonded to the film. The method arranges a lead wire of the wiring member on the film, and arranges a metal bypass member on the film. A pair of welding electrodes are connected with the lead wire, and then welding the lead wire to the film occurs by allowing electric current to flow between the pair of welding electrodes.