An onboard wireless communication system includes a power supply circuit, a wireless communication circuit, a control circuit, and a current integration circuit. The current integration circuit calculates an integration value of current fed from a battery after the battery starts discharging. The current integration circuit temporarily stops the calculation until transmission of a burglar alarm signal is completed when a burglar detection signal is outputted from a burglar detection ECU while the integration value is still smaller than a reference value. As a result, power supply from the power supply circuit to the wireless communication circuit is maintained. The power supply is stopped when the integration value is equal to or larger than the reference value while the burglar detection signal is still not outputted from the burglar detection ECU.