A tire position determination system includes a tire pressure detector attached to each tire to generate a tire pressure signal. An acceleration detector generates gravitational information for each tire pressure detector. A receiver arranged in a vehicle body receives the tire pressure signal from each tire pressure detector. An axle rotation amount detector detects an axle rotation amount of an axle corresponding to each tire and generates pulses indicative of the detected axle rotation amount. An automatic locator determines the position of each tire based on the gravitational force and the pulses. A pulse combination determination unit determines whether or not a combination of the pulses from the axle rotation amount detectors is appropriate. A pulse acquisition timing setting unit sets an acquisition timing of the pulse signal for the automatic locator based on the determination of the pulse combination determination unit.