A tire-pressure control apparatus includes time calculation means for calculating an up time over which the tire pressure of each wheel increases from a lower limit set value to an upper limit set value and a down time over which the tire pressure of the wheel decreases from the upper limit set value to the lower limit set value, on the basis of the detection value of a corresponding pressure sensor; average-rotational-speed calculation means for calculating an average rotational speed of the wheel during the up time on the basis of the detection value of a corresponding wheel speed sensor; first-pump-supplied-air-quantity calculation means (403) for calculating a first pump-supplied air quantity Qvw* of a corresponding air pressure generation unit in a single generation and non-generation cycle on the basis of the up time and the average rotational speed; second-pump-supplied-air-quantity calculation means (404) for calculating a second pump-supplied air quantity Qp* of the air pressure generation unit in a single generation and non-generation cycle on the basis of the up time and the down time; and determination means (405) for comparing the first pump-supplied air quantity Qvw* and the second pump-supplied air quantity Qp*.