A thermal insulation sheet includes a heat storage sheet, an insulation sheet affixed to the heat storage sheet, and a highly-thermoconductive sheet affixed to the insulation sheet. The heat storage sheet contains a resin and powdery microcapsules mixed with the resin. The powdery microcapsules encapsulate latent-heat storage agent. The heat storage sheet has a void ratio not less than 10% and not more than 30%. Or, the heat storage sheet may have surface roughness Ra not less than 2 μm and not more than 20 μm. The thermal insulation sheet suppresses or retards transferring of heat generated in a heat-generating component to outside, and suppresses a rapid rising of a temperature of the heat-generating component.