A temperature-raising device for an in-car battery includes: a battery temperature acquisition unit configured to acquire a temperature of a battery mounted in a vehicle; an environmental temperature acquisition unit configured to acquire an environmental temperature; a heater configured to raise the temperature of the battery; and a controller configured to i) turn ON or OFF the heater based on a result of a comparison between the battery temperature acquired by the battery temperature acquisition unit and a predetermined threshold, and ii) reduce the threshold in accordance with a reduction in the environmental temperature acquired by the environmental temperature acquisition unit.