Tire air pressure monitoring device, vehicle including tire air pressure monitoring device, and tire air pressure monitoring method

Each time identification information specific to each of wheels is received, a rotation position of each of the wheels is obtained and accumulated as rotation position data of each wheel with respect to each piece of identification information. Then, with respect to all the identification information, when a first tentative mounting position and a second tentative mounting position are the same in a vehicle width direction and different from each other in a vehicle longitudinal direction, the first and second tentative mounting positions being mounting positions of two of the wheels where a smallest degree of dispersion and a second smallest degree of dispersion are detected, and when the first tentative mounting position determined for each piece of the identification information is different from one another, each first tentative mounting position is determined as the mounting position of each of the wheels corresponding to the identification information, respectively.