A seat heater device operable to initiate power supply upon operation of a switch by a seat occupant within a vehicle interior, the seat heater device comprising: a heater for warming installed in a seat within the vehicle interior; and a control unit operable to control energization of the heater for warming, the control unit comprising: a low-voltage detecting means operable to detect whether a drive voltage of the control unit is a regular drive voltage value of the control unit or a voltage value lower than a predetermined voltage value and to output an energization signal when the regular drive voltage value is detected and to output an energization disable instruction when the voltage value lower than a predetermined voltage value is detected; and a switching element that is turned on when the low-voltage detecting means detects the regular drive voltage value of the control unit, wherein the control unit is operable to receive said energization instruction from the low-voltage detecting means to turn on the switching element when the low-voltage detecting means detects the regular drive voltage, wherein the control unit is further operable to receive said energization disable instruction from the low-voltage detecting means to prevent turning on the switching element when the low-voltage detecting means detects a voltage value lower than the predetermined voltage value, and wherein the switching element has a feature of increasing an internal resistance with a reduction in a drive signal of the switching element, and the drive voltage of the control unit reduces thereby reducing the drive signal voltage of the switching element. a heater for warming installed in a seat within the vehicle interior; and a control unit operable to control energization of the heater for warming, the control unit comprising: a low-voltage detecting means operable to detect whether a drive voltage of the control unit is a regular drive voltage value of the control unit or a voltage value lower than a predetermined voltage value and to output an energization signal when the regular drive voltage value is detected and to output an energization disable instruction when the voltage value lower than a predetermined voltage value is detected; and a switching element that is turned on when the low-voltage detecting means detects the regular drive voltage value of the control unit, a low-voltage detecting means operable to detect whether a drive voltage of the control unit is a regular drive voltage value of the control unit or a voltage value lower than a predetermined voltage value and to output an energization signal when the regular drive voltage value is detected and to output an energization disable instruction when the voltage value lower than a predetermined voltage value is detected; and a switching element that is turned on when the low-voltage detecting means detects the regular drive voltage value of the control unit, wherein the control unit is operable to receive said energization instruction from the low-voltage detecting means to turn on the switching element when the low-voltage detecting means detects the regular drive voltage, wherein the control unit is further operable to receive said energization disable instruction from the low-voltage detecting means to prevent turning on the switching element when the low-voltage detecting means detects a voltage value lower than the predetermined voltage value, and wherein the switching element has a feature of increasing an internal resistance with a reduction in a drive signal of the switching element, and the drive voltage of the control unit reduces thereby reducing the drive signal voltage of the switching element.