A battery temperature control device for temperature-controlling by heating a battery with a heater when the battery becomes less than a predetermined temperature (Tbat1), characterized by: a battery-temperature fall time prediction means (S13, S14) for predicting, based on a combination of a temperature (Tbat) of the battery and an outside air temperature (Tatm), a predictive time (Δt) that the temperature (Tbat) of the battery is predicted to fall to less than the predetermined temperature (Tbat1), which is a first set temperature (Tbat1) higher than a freezing point of a battery electrolyte which is a temperature at which an inputable/outputable electronic power becomes 0, such that the battery temperature control device shifts to a sleep state after the predictive time (Δt) has been predicted; and a heating necessity determination means for determining a necessity of heating with the heater by starting up the battery temperature control device from the sleep state and by determining whether or not the temperature (Tbat) of the battery is less than the predetermined temperature (Tbat1) when the predictive time (Δt), predicted by the battery-temperature fall time prediction means, has expired, wherein the battery temperature control device is configured to re-predict the predictive time (Δt) and to maintain the sleep state, when the temperature (Tbat) of the battery is determined to be higher than or equal to the predetermined temperature (Tbat1) by the heating necessity determination means, upon expiration of the predictive time (Δt), and wherein the battery temperature control device is configured to temperature-control by heating the battery with the heater, only when the temperature (Tbat) of the battery is determined to be less than the predetermined temperature (Tbat1) by the heating necessity determination means, the temperature (Tbat) of the battery is higher than or equal to a second set temperature (Tbat2) higher than the temperature at which the inputable/outputable electronic power becomes 0 and also less than the first predetermined temperature (Tbat1), and a state of charge of the battery is greater than or equal to a set value (SOCs) that can activate the heater, upon expiration of the predictive time (Δt). a battery-temperature fall time prediction means (S13, S14) for predicting, based on a combination of a temperature (Tbat) of the battery and an outside air temperature (Tatm), a predictive time (Δt) that the temperature (Tbat) of the battery is predicted to fall to less than the predetermined temperature (Tbat1), which is a first set temperature (Tbat1) higher than a freezing point of a battery electrolyte which is a temperature at which an inputable/outputable electronic power becomes 0, such that the battery temperature control device shifts to a sleep state after the predictive time (Δt) has been predicted; and a heating necessity determination means for determining a necessity of heating with the heater by starting up the battery temperature control device from the sleep state and by determining whether or not the temperature (Tbat) of the battery is less than the predetermined temperature (Tbat1) when the predictive time (Δt), predicted by the battery-temperature fall time prediction means, has expired, wherein the battery temperature control device is configured to re-predict the predictive time (Δt) and to maintain the sleep state, when the temperature (Tbat) of the battery is determined to be higher than or equal to the predetermined temperature (Tbat1) by the heating necessity determination means, upon expiration of the predictive time (Δt), and wherein the battery temperature control device is configured to temperature-control by heating the battery with the heater, only when the temperature (Tbat) of the battery is determined to be less than the predetermined temperature (Tbat1) by the heating necessity determination means, the temperature (Tbat) of the battery is higher than or equal to a second set temperature (Tbat2) higher than the temperature at which the inputable/outputable electronic power becomes 0 and also less than the first predetermined temperature (Tbat1), and a state of charge of the battery is greater than or equal to a set value (SOCs) that can activate the heater, upon expiration of the predictive time (Δt).