An apparatus for controlling tire inflation pressure includes an outlet side end portion of a supplying passageway opened on an outer circumference of a column-shaped boss portion provided in an axle, and an inlet side end portion of an introducing passageway that is opened on an inner circumference of an annular hub portion provided in a wheel. A wheel is mounted onto the axle. The inner circumference of the annular hub portion is engaged with the outer circumference of the column-shaped boss portion, and thereby the outlet side end portion and the inlet side end portion are communicatively connected to each other air tightly. Thus, easiness in mounting a vehicle wheel assembly relative to the axle can be improved.