To solve such an inconvenience that a smart entry device can not be used when a battery capacity is consumed in a place where cells are hardly obtained, since cells are used for a radio device.

The radio device has a transponder and a keyless circuit and a portable transceiver outputting a high frequency ID code to a vehicle side transceiver when the keyless circuit receives a low frequency request electromagnetic wave signal from the vehicle side transceiver, and outputting a low frequency ID code to the vehicle side transceiver when the transponder receives electromagnetic waves for a low frequency power. When the vehicle side transceiver receives a high frequency ID code or a low frequency ID code, it decodes the ID code and when the ID code is judged to be normal, at least a signal for enabling engine start is outputted.