To allow a visible light ray to be useful in a therapy of an affected part or other concealed disease without irradiating the affected part directly with the visible light by conveniently treating the affected part of a body by utilizing the heating action of the light generated by an arc discharge.

The photodynamic therapeutic device irradiates with the visible light by the arc discharge between a pair of carbon electrode bars and irradiates the skin of the shoulder of the dominant arm side of the body with the visible light. A visible light irradiating port 12 for laterally irradiating with the visible light generated by the arc discharge is opened in a case 10 which contains the carbon electrode bars 11. The opening area of the port 12 can be made enlarged and contracted.