An electrical tree test method of testing for electrical trees in an insulating member including a mica insulation applied to an electrical conductor, the method comprising: a power supply connecting step of connecting an electrical conductor and an electrode structure to a power supply in order to apply a voltage between the electrical conductor and the electrode structure; and a voltage applying step of applying a voltage between the electrical conductor and the electrode structure, after the power connecting step, characterized in that the method further comprises, before the power supply connecting step, a set setting step of attaching an electrode setting set including an electrode setting assembly and two insulation spacers to outside of the mica insulation; an impregnation step of impregnating the mica insulation with synthetic resin after the set setting step; and a removal step of removing components of the electrode setting set, except an electrode structure, after the impregnation step, wherein the electrode structure includes a substrate having an electrically conductive surface and a second surface at the back side of the first surface that are flat and parallel to each other, and a plurality of electrically conductive needle electrodes disposed on the first surface of the substrate and located with circumferential intervals therebetween, the electrodes setting set includes the electrode structure, electrode setting assembly including a first electrode spacer having a first surface and a second surface at the back side of the first surface that are flat and parallel to each other and thickness thereof are equal to that of the substrate, a second electrode spacer having a first surface and a second surface at the back side of the first surface that are flat and parallel to each other and thickness thereof are equal to that of the substrate, and a holding plate having a first surface formed to be flat, and the insulation spacers that are arranged at both axial sides of the electrode structure and control distances between the mica insulation and distal ends of the needle electrodes. a power supply connecting step of connecting an electrical conductor and an electrode structure to a power supply in order to apply a voltage between the electrical conductor and the electrode structure; and a voltage applying step of applying a voltage between the electrical conductor and the electrode structure, after the power connecting step, characterized in that the method further comprises, before the power supply connecting step, a set setting step of attaching an electrode setting set including an electrode setting assembly and two insulation spacers to outside of the mica insulation; an impregnation step of impregnating the mica insulation with synthetic resin after the set setting step; and a removal step of removing components of the electrode setting set, except an electrode structure, after the impregnation step, wherein the electrode structure includes a substrate having an electrically conductive surface and a second surface at the back side of the first surface that are flat and parallel to each other, and a plurality of electrically conductive needle electrodes disposed on the first surface of the substrate and located with circumferential intervals therebetween, a substrate having an electrically conductive surface and a second surface at the back side of the first surface that are flat and parallel to each other, and a plurality of electrically conductive needle electrodes disposed on the first surface of the substrate and located with circumferential intervals therebetween, the electrodes setting set includes the electrode structure, electrode setting assembly including a first electrode spacer having a first surface and a second surface at the back side of the first surface that are flat and parallel to each other and thickness thereof are equal to that of the substrate, a second electrode spacer having a first surface and a second surface at the back side of the first surface that are flat and parallel to each other and thickness thereof are equal to that of the substrate, and a holding plate having a first surface formed to be flat, and the electrode structure, electrode setting assembly including a first electrode spacer having a first surface and a second surface at the back side of the first surface that are flat and parallel to each other and thickness thereof are equal to that of the substrate, a second electrode spacer having a first surface and a second surface at the back side of the first surface that are flat and parallel to each other and thickness thereof are equal to that of the substrate, and a holding plate having a first surface formed to be flat, and a first electrode spacer having a first surface and a second surface at the back side of the first surface that are flat and parallel to each other and thickness thereof are equal to that of the substrate, a second electrode spacer having a first surface and a second surface at the back side of the first surface that are flat and parallel to each other and thickness thereof are equal to that of the substrate, and a holding plate having a first surface formed to be flat, and the insulation spacers that are arranged at both axial sides of the electrode structure and control distances between the mica insulation and distal ends of the needle electrodes.