An air pressure warning device of a vehicle tire has an excessive/deficient amount calculation module (10b) for calculating an excessive/deficient amount on the basis of the difference between a normal air pressure stored in a normal air pressure storage module (10a) and a detected tire air pressure, an informing control module (10c) for controlling an informing module (11) to inform an excessive/deficient state of the tire air pressure determined based on the calculated excessive/deficient amount, and a normal air pressure correction module 10e for increasing the readout normal air pressure by a predetermined value when an expressway traveling detection module (10d) detects that the vehicle is on an expressway.