A photomultiplier tube comprising: a vacuum vessel having a faceplate constituting one end and a stem constituting another end; a photocathode that converts incident light incident through the faceplate to electrons; an electron multiplying section that multiplies the electrons emitted from the photocathode; and an electron detecting section that transmits output signals in response to electrons from the electron multiplying section, wherein the photocathode, the electron multiplying section, and the electron detecting section are provided within the vacuum vessel, wherein the electron multiplying section includes an electrode-layered unit in which electrodes including dynodes (Dy1-Dy12) are stacked in a plurality of stages, wherein the stem is made from an insulating member having a first surface provided at an inner side of the vacuum vessel, a second surface that opposes the first surface, and a peripheral section that connects the first surface and the second surface, the photomultiplier tube further comprises: a tubular member that surrounds the peripheral section; and an extending section that extends from the tubular member and that is formed with openings (22, 48) therein, wherein the extending section is made of a metal; and potential applying pins (21, 47) penetrate the openings (22, 48) and are fixed to the stem, the potential applying pin (21, 47) applying potentials to the electrode-layered unit, characterized in that the extending section extends along the first surface of the stem, and the extending section covers a peripheral region of the first surface of the stem. a vacuum vessel having a faceplate constituting one end and a stem constituting another end; a photocathode that converts incident light incident through the faceplate to electrons; an electron multiplying section that multiplies the electrons emitted from the photocathode; and an electron detecting section that transmits output signals in response to electrons from the electron multiplying section, wherein the photocathode, the electron multiplying section, and the electron detecting section are provided within the vacuum vessel, wherein the electron multiplying section includes an electrode-layered unit in which electrodes including dynodes (Dy1-Dy12) are stacked in a plurality of stages, wherein the stem is made from an insulating member having a first surface provided at an inner side of the vacuum vessel, a second surface that opposes the first surface, and a peripheral section that connects the first surface and the second surface, the photomultiplier tube further comprises: a tubular member that surrounds the peripheral section; and an extending section that extends from the tubular member and that is formed with openings (22, 48) therein, wherein the extending section is made of a metal; and a tubular member that surrounds the peripheral section; and an extending section that extends from the tubular member and that is formed with openings (22, 48) therein, wherein the extending section is made of a metal; and potential applying pins (21, 47) penetrate the openings (22, 48) and are fixed to the stem, the potential applying pin (21, 47) applying potentials to the electrode-layered unit, characterized in that the extending section extends along the first surface of the stem, and the extending section covers a peripheral region of the first surface of the stem.