Abstract: An apparatus for regulating the pneumatic pressure of a tire according to the invention calculates the pressure difference between the specified pneumatic pressure entered therein through an input section and the actual pneumatic pressure of a tire measured by a pressure sensor and operates its air charging or discharging valve by specifying an extent of openness of the valve and a time for keeping the valve open as a function of the obtained pressure difference. Thereafter, it calculates the rate of change in the pneumatic pressure of the tire from the actual pneumatic pressure of the tire measured for the second time during the valve is kept open and, at the same time, the pressure difference between the specified pneumatic pressure value and the actual pneumatic pressure of the tire measured for the second time.