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) that constitute a plurality of channels are stacked in a plurality of stages in a stacking direction (z), wherein the plurality of stages of electrodes (17, Dy1-Dy12, 19) is stacked with an insulator interposed between two adjacent electrodes; wherein the electron detecting section includes a plurality of anodes that is arranged spaced away from and in confrontation with a last stage electrode of the electrode-layered unit and that is arranged in association with the channels; and wherein the stem is provided with supporting means for supporting the electrode-layered unit, the supporting means defining an axis extending in the stacking direction, wherein the supporting means comprises: a supporting section inserted into the stem and extending in the stacking direction (z); and a placing section provided at an upper end of the supporting section for placing the last stage electrode; a cross-sectional area of the placing section in a plane perpendicular to the stacking direction (z) is larger than a cross-sectional area of the supporting section in a plane perpendicular to the stacking direction (z); and the insulator, the supporting section and the placing section are arranged coaxially on the axis of the supporting means. 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) that constitute a plurality of channels are stacked in a plurality of stages in a stacking direction (z), wherein the plurality of stages of electrodes (17, Dy1-Dy12, 19) is stacked with an insulator interposed between two adjacent electrodes; wherein the electron detecting section includes a plurality of anodes that is arranged spaced away from and in confrontation with a last stage electrode of the electrode-layered unit and that is arranged in association with the channels; and wherein the stem is provided with supporting means for supporting the electrode-layered unit, the supporting means defining an axis extending in the stacking direction, wherein the supporting means comprises: a supporting section inserted into the stem and extending in the stacking direction (z); and a placing section provided at an upper end of the supporting section for placing the last stage electrode; a cross-sectional area of the placing section in a plane perpendicular to the stacking direction (z) is larger than a cross-sectional area of the supporting section in a plane perpendicular to the stacking direction (z); and the insulator, the supporting section and the placing section are arranged coaxially on the axis of the supporting means.