A battery temperature regulating apparatus includes an onboard battery, a temperature regulating plate, a heat exchanger including a container and a first internal passage, first to third passages, a radiator, a valve, a temperature sensor, and a control device including a processor and a memory. The processor is configured to execute, in cooperation with a program included in the memory, a process including determining whether a temperature of the onboard battery is higher than an upper threshold of a proper temperature range, determining whether a heat source is in the container at least based on the temperature of a first heat medium detected by the temperature sensor, and if the temperature of the onboard battery is higher than the upper threshold and that the heat source is in the container, controlling the valve in such a way as to allow the first heat medium to flow through the heat exchanger.