A tire condition monitoring apparatus with a keyless entry function, comprising: a keyless entry portable communication device capable of transmitting and receiving signals; a plurality of sensor units each being attachable to a wheel of the vehicle, each sensor unit detecting the condition of a tire attached to the wheel and transmitting a condition data signal that contains data representing the detected tire condition, wherein, in response to the reception of a command signal the sensor unit can execute operation in accordance with the command content in the command signal; a plurality of antennas each arrangeable in the vehicle body to correspond to one of the wheels; and a control unit locatable in the vehicle body and connected to the antennas, the control unit when operated executing a keyless entry function based on transmission and reception of signals with the portable communication device via at least one of the antennas, and the control unit transmitting the command signal to each of the sensor units via the corresponding antenna and processing the condition data signal received from each of the sensor units via the corresponding antenna, characterized in that the keyless entry portable communication device is arranged to transmit and receive high frequency signals, in that each sensor unit is arranged to transmit the condition data signal in the form of a high frequency signal, in that the control unit is arranged to execute the keyless entry function based on transmission and reception of high frequncy signals with the portable communication device via the at least one of the antennas, and in that the control unit is arranged to transmit the command signal in the form of a high frequency signal to each of the sensor units via the corresponding antenna. a keyless entry portable communication device capable of transmitting and receiving signals; a plurality of sensor units each being attachable to a wheel of the vehicle, each sensor unit detecting the condition of a tire attached to the wheel and transmitting a condition data signal that contains data representing the detected tire condition, wherein, in response to the reception of a command signal the sensor unit can execute operation in accordance with the command content in the command signal; a plurality of antennas each arrangeable in the vehicle body to correspond to one of the wheels; and a control unit locatable in the vehicle body and connected to the antennas, the control unit when operated executing a keyless entry function based on transmission and reception of signals with the portable communication device via at least one of the antennas, and the control unit transmitting the command signal to each of the sensor units via the corresponding antenna and processing the condition data signal received from each of the sensor units via the corresponding antenna, characterized in that the keyless entry portable communication device is arranged to transmit and receive high frequency signals, in that each sensor unit is arranged to transmit the condition data signal in the form of a high frequency signal, in that the control unit is arranged to execute the keyless entry function based on transmission and reception of high frequncy signals with the portable communication device via the at least one of the antennas, and in that the control unit is arranged to transmit the command signal in the form of a high frequency signal to each of the sensor units via the corresponding antenna.