PURPOSE: To shorten the cranking time sharply by allowing both No.1 and No.2 connecting means to be applied so as to heat up both glow plugs and air for combustion when an engine is preheated.

CONSTITUTION: When a key switch 2 is turned on, a control device 8 allows a starter indicating lamp 84 to be turned on, and simultaneously allows No.1 and No.2 relays 6b and 7b to be excited for closing their contacts 6a and 7a so as to apply electric current both of glow plugs 3 and an air heater 5. Then after a specified period of time has elapsed to heat the glow plugs 3 up to 1,000°C, the start indicating lamp 84 is turned off by its timer signal informing a driver of the start of cranking. Then, when the key switch 2 is connected to a ST terminal, an engine starting is initiated for allowing fuel to burn satisfactorily because intake air is heated and fuel is vaporized due to the increase in temperature. When the engine starts running, an electric charge detecting terminal 81 is turned on allowing a charge lamp 85 to be turned on for giving information to the driver. Thus, this configuration can shorten the cranking time sharply.