A tire pneumatic pressure monitoring device, comprising: a tire pneumatic pressure sensor installed on a tire of each wheel to detect a tire pneumatic pressure acting on the tire; an acceleration sensor installed on the tire of each wheel to detect an acceleration in a prescribed direction acting on the tire; a transmitter arranged on each wheel to detect a rotational position of the wheel based on a detected value of the acceleration sensor for transmitting the pneumatic pressure along with a specific identification information unique to each transmitter via a wireless signal; a receiver installed on a vehicle body to receive the wireless signal; and a rotational position detection unit installed on the vehicle body to detect the rotational position of each wheel when the specific identification information has been transmitted; characterized by a wheel position determination unit that acquires the rotational position of each wheel a plurality of times to accumulate the rotational position data for each wheel and determines a wheel position corresponding to the rotational position data with a least dispersion degree among the rotational position data of the wheel position of the transmitter corresponding to the specific identification information and a detection inhibition unit that inhibits the accumulation of the rotational position data of each wheel by the rotational position detection unit when a braking control to control a wheel cylinder pressure of the wheel is being executed, wherein the wheel position determination unit that converts the rotational position of the wheel to a vector on a two-dimensional plane with its origin as a starting point and a circumferential point of a unit circle as an ending point, calculates a scalar quantity of an average vector of each rotational position data as a dispersion characteristic value, and determines a maximum value of each dispersion characteristic value as that with the least dispersion degree. a tire pneumatic pressure sensor installed on a tire of each wheel to detect a tire pneumatic pressure acting on the tire; an acceleration sensor installed on the tire of each wheel to detect an acceleration in a prescribed direction acting on the tire; a transmitter arranged on each wheel to detect a rotational position of the wheel based on a detected value of the acceleration sensor for transmitting the pneumatic pressure along with a specific identification information unique to each transmitter via a wireless signal; a receiver installed on a vehicle body to receive the wireless signal; and a rotational position detection unit installed on the vehicle body to detect the rotational position of each wheel when the specific identification information has been transmitted; characterized by a wheel position determination unit that acquires the rotational position of each wheel a plurality of times to accumulate the rotational position data for each wheel and determines a wheel position corresponding to the rotational position data with a least dispersion degree among the rotational position data of the wheel position of the transmitter corresponding to the specific identification information and a detection inhibition unit that inhibits the accumulation of the rotational position data of each wheel by the rotational position detection unit when a braking control to control a wheel cylinder pressure of the wheel is being executed, wherein the wheel position determination unit that converts the rotational position of the wheel to a vector on a two-dimensional plane with its origin as a starting point and a circumferential point of a unit circle as an ending point, calculates a scalar quantity of an average vector of each rotational position data as a dispersion characteristic value, and determines a maximum value of each dispersion characteristic value as that with the least dispersion degree.