A heat insulating structure of an electric component comprising: a fixing member provided with a placement part having a placement surface on which an electric component is placed; a cover member including a cover-side ceiling wall and a plurality of cover-side side walls (23B, 23C, 23D, 23E) extending downward from the cover-side ceiling wall, the cover member being configured to cover the fixing member and the electric component from above and from a side; and a heat insulating member including a heat-insulating-member-side ceiling wall and at least one heat-insulating-member-side side wall extending downward from the heat-insulating-member-side ceiling wall, the heat insulating member being provided between the cover member and the electric component, the heat insulating structure being characterised by: the fixing member being fixed to a fixed part (7A, 7B) provided on an upper surface of a floor panel of a vehicle and the fixing member is located at a position where the placement surface is higher than the floor panel; and the cover member includes a first support part, a second support part and a third support part, the first support part (23 S) is provided on the cover-side ceiling wall and is in contact with one end portion of the heat-insulating-member-side ceiling wall in a direction in which the heat-insulating-member-side ceiling wall extends, the second support part is provided on a predetermined cover-side side wall facing the heat-insulating-member-side side wall of the plurality of cover-side side walls (23B, 23C, 23D, 23E) and is in contact with one end portion of the heat-insulating-member-side side wall in a direction in which the heat-insulating-member-side side wall extends, the third support part is provided on the predetermined cover-side side wall and is in contact with a bottom end portion orthogonal to the direction in which the heat-insulating-member-side side wall extends. a fixing member provided with a placement part having a placement surface on which an electric component is placed; a cover member including a cover-side ceiling wall and a plurality of cover-side side walls (23B, 23C, 23D, 23E) extending downward from the cover-side ceiling wall, the cover member being configured to cover the fixing member and the electric component from above and from a side; and a heat insulating member including a heat-insulating-member-side ceiling wall and at least one heat-insulating-member-side side wall extending downward from the heat-insulating-member-side ceiling wall, the heat insulating member being provided between the cover member and the electric component, the heat insulating structure being characterised by: the fixing member being fixed to a fixed part (7A, 7B) provided on an upper surface of a floor panel of a vehicle and the fixing member is located at a position where the placement surface is higher than the floor panel; and the cover member includes a first support part, a second support part and a third support part, the first support part (23 S) is provided on the cover-side ceiling wall and is in contact with one end portion of the heat-insulating-member-side ceiling wall in a direction in which the heat-insulating-member-side ceiling wall extends, the second support part is provided on a predetermined cover-side side wall facing the heat-insulating-member-side side wall of the plurality of cover-side side walls (23B, 23C, 23D, 23E) and is in contact with one end portion of the heat-insulating-member-side side wall in a direction in which the heat-insulating-member-side side wall extends, the third support part is provided on the predetermined cover-side side wall and is in contact with a bottom end portion orthogonal to the direction in which the heat-insulating-member-side side wall extends. the fixing member being fixed to a fixed part (7A, 7B) provided on an upper surface of a floor panel of a vehicle and the fixing member is located at a position where the placement surface is higher than the floor panel; and the cover member includes a first support part, a second support part and a third support part, the first support part (23 S) is provided on the cover-side ceiling wall and is in contact with one end portion of the heat-insulating-member-side ceiling wall in a direction in which the heat-insulating-member-side ceiling wall extends, the second support part is provided on a predetermined cover-side side wall facing the heat-insulating-member-side side wall of the plurality of cover-side side walls (23B, 23C, 23D, 23E) and is in contact with one end portion of the heat-insulating-member-side side wall in a direction in which the heat-insulating-member-side side wall extends, the third support part is provided on the predetermined cover-side side wall and is in contact with a bottom end portion orthogonal to the direction in which the heat-insulating-member-side side wall extends.