A tire air pressure abnormality warning device includes a transmitter for transmitting a signal of the air pressure of a tire measured by a pressure sensor, a portable device for opening and closing a door lock of a vehicle, and a vehicle-installed device for determining whether or not the signal from the transmitter indicates an abnormal air pressure of the tire and for driving the door lock by a signal from the portable device. The vehicle-installed device has a recording section for recording tire air pressure abnormality data. When the vehicle-installed device communicates with the portable device, it searches for any abnormality data from the recording section. If there is any abnormality data, it transmits a tire air pressure abnormality signal to the portable device. The portable device indicates a warning of abnormal air pressure of the tire by the tire air pressure abnormality signal using a warning indicating section.