Provided are a photocathode plate capable of stably achieving a high sensitive property, and an electron tube using such a photocathode plate.In a photomultiplier tube 1, an insulating layer 63 is formed between a semiconductor electron emission layer 51 in a photocathode plate 23A, and a first electrode 65 electrically connected to an electron releasing portion 59. This insulating layer 63 permits the photocathode plate 23A to be cleaned by heat cleaning at a high temperature, in a stage before formation of an active layer 61 on an exposed region of the semiconductor electron emission layer 51 in the electron releasing portion 59. This makes it feasible to effectively clean the exposed region of the semiconductor electron emission layer 51 in the electron releasing portion 59 and to stabilize the physical properties of the exposed region. In consequence, a higher sensitive property can be stably achieved in the photocathode plate 23A and in the photomultiplier tube 1 using the photocathode plate 23A.