A tire air pressure monitoring system for a vehicle is disclosed. The tire air pressure monitoring system includes a detector configured to detect tire air pressures of tires of the vehicle; and a processing device. The processing device is configured to output a first notification that is an alarm representing a reduced tire air pressure state based on at least one of the tire air pressures less than or equal to a first threshold, detect a predetermined opportunity at which the tires can be filled with air, and output a second notification, differently from the first notification, based on a detection of the predetermined opportunity and at least one of the tire air pressures less than or equal to a second threshold but greater than the first threshold, the second threshold being greater than the first threshold.