An object is to sufficiently keep the airtightness in a vacuum container even when it is made smaller. A photomultiplier tube 1 comprises a flat sheet-like lower substrate 4, a casing-like frame 3b erected on the lower substrate 4, an upper substrate 2 including a frame 3a airtightly joined to an opening part of the frame 3b while holding a low-melting metal therebetween, and a frame-like projection 25b arranged in parallel with the frame 3b on the inner side of the frame 3b on the lower substrate 4.