An in-vehicle wireless communication device stores calibration information used in combination with a radio wave intensity of a mobile terminal in a state of identifying the mobile terminal, performs wireless communication with the mobile terminal in a state of identifying the mobile terminal, detects the radio wave intensity of a radio wave received from the mobile terminal during the wireless communication, and detects distance information to the mobile terminal based on the radio wave intensity of the radio wave received from the mobile terminal and the calibration information stored for the mobile terminal.