To increase the reliability of the retention of airtightness of a tire air chamber.

The tire air pressure adjustment device 30 adjusts the air pressure in the tire according to a pressure difference between the air pressure in the tire and the air pressure supplied from a vehicle body side. A first block includes a valve for increasing the air pressure in the tire. A second block includes a valve for decreasing the air pressure in the tire. A third block retains the air pressure in the tire. The third block is selected in a state where the atmosphere pressure is being supplied from a vehicle side. The first block is selected in a state where the higher air pressure than the air pressure in the tire is being supplied from the vehicle side. The second block is selected in a state where the lower air pressure than the air pressure in the tire by a predetermined value is being supplied from the vehicle side.