ELECTRON TUBE

An electron tube 1 includes a photoelectric surface 3 that emits electrons E corresponding to light L, an avalanche photodiode 6 that is disposed to face the photoelectric surface 3, a focusing electrode part 4 that accelerates and focuses the electrons E from the photoelectric surface 3 toward the avalanche photodiode 6, and a casing 2 including a stem 9 provided with the avalanche photodiode 6. The stem 9 is provided with a light incident hole 26 through which the light L is transmitted, and the periphery of the light incident hole 26 is light-shielded by the stem 9. The focusing electrode part 4 includes a first region 34a provided with a light passage hole 37, and a second region 34b provided with an electron passage hole 38 that guides the electrons E to the avalanche photodiode 6. The first region 34a is formed on an axial line A1 that connects the light incident hole 26 and the photoelectric surface 3. The second region 34b is formed on an axial line A1 that connects the photoelectric surface 3 and the avalanche photodiode 6.