A power supply device for a spacecraft, the power supply device comprising: an electric component; a substrate on which the electric component is mounted on a mounting surface; a chassis having a chassis surface facing a back surface of the substrate which is the opposite side of the mounting surface and a threaded part; a chassis-side resin part being an insulating resin-cured material to be placed between the back surface of the substrate and the chassis surface so as to be connected to the back surface and the chassis surface; a fixation screw having a threaded shaft part; and an insulating member through which an open hole in which the fixation screw is placed is formed, wherein open holes (25d, 20d) are formed through the electric component and the substrate, the insulating member includes a first placement part placed in a space formed by continuous placement of the open hole of the electric component and the open hole of the substrate and a second placement part placed outside the open hole of the electric component so as to be in contact with a peripheral edge of the open hole of the electric component, the fixation screw fixes both the electric component and the substrate to the chassis by screw-coupling an end part of the threaded shaft part, exposed in a direction toward the chassis from the open hole of the insulating member, to the threaded part of the chassis and brings the electric component and the chassis into electrical noncontact with each other by being placed in the open hole of the insulating member, characterised in that: the cured insulating resin has a thermal conductivity between 1 W/mK and 10 W/mK inclusive; the substrate includes a plurality of filled through-holes in which a plurality of through-holes penetrate from a region on the back surface directly beneath the electric component to the mounting surface, and which through-holes are filled with a heat transfer material such that a potential at a ground terminal of the electric component and a potential on the chassis are kept at different potentials and such that the heat of the electric component is conducted to the chassis. an electric component; a substrate on which the electric component is mounted on a mounting surface; a chassis having a chassis surface facing a back surface of the substrate which is the opposite side of the mounting surface and a threaded part; a chassis-side resin part being an insulating resin-cured material to be placed between the back surface of the substrate and the chassis surface so as to be connected to the back surface and the chassis surface; a fixation screw having a threaded shaft part; and an insulating member through which an open hole in which the fixation screw is placed is formed, wherein open holes (25d, 20d) are formed through the electric component and the substrate, the insulating member includes a first placement part placed in a space formed by continuous placement of the open hole of the electric component and the open hole of the substrate and a second placement part placed outside the open hole of the electric component so as to be in contact with a peripheral edge of the open hole of the electric component, the fixation screw fixes both the electric component and the substrate to the chassis by screw-coupling an end part of the threaded shaft part, exposed in a direction toward the chassis from the open hole of the insulating member, to the threaded part of the chassis and brings the electric component and the chassis into electrical noncontact with each other by being placed in the open hole of the insulating member, characterised in that: the cured insulating resin has a thermal conductivity between 1 W/mK and 10 W/mK inclusive; the substrate includes a plurality of filled through-holes in which a plurality of through-holes penetrate from a region on the back surface directly beneath the electric component to the mounting surface, and which through-holes are filled with a heat transfer material such that a potential at a ground terminal of the electric component and a potential on the chassis are kept at different potentials and such that the heat of the electric component is conducted to the chassis. the cured insulating resin has a thermal conductivity between 1 W/mK and 10 W/mK inclusive; the substrate includes a plurality of filled through-holes in which a plurality of through-holes penetrate from a region on the back surface directly beneath the electric component to the mounting surface, and which through-holes are filled with a heat transfer material such that a potential at a ground terminal of the electric component and a potential on the chassis are kept at different potentials and such that the heat of the electric component is conducted to the chassis.