A vacuum vessel is configured by hermetically joining a faceplate to one end of a side tube and a stem to the other end via a tubular member. A photocathode, a focusing electrode, dynodes, a drawing electrode, and anodes are arranged within the vacuum vessel. At the center of the stem an air discharging tube is connected. The air discharging tube includes an outer side tube and an inner side tube, which are disposed coaxially and connected to each other at the stem side. The outer side tube has high adhesiveness with the stem and the inner side tube is thin and has small stress when being cut, thereby enabling the joint with the vacuum vessel not to be damaged when the air discharging tube is sealed.