A method and an apparatus configured to acquire, as acceleration information, a peak level ak which is a magnitude of a peak on a positive side or a negative side of an acceleration signal in a tire circumferential direction or a tire width direction detected by an acceleration sensor, or a peak interval bk which is a time interval between peaks, or acquire the peak level ak or the peak interval bk of a differential acceleration signal in a tire radial direction obtained by differentiating the acceleration signal in the tire radial direction; calculate ratios Pk, Qk of a difference between the acquired acceleration information ak, bk and average values Ak−1 of the acceleration information to the average values; and determine that the acceleration sensor is detached from the inside of the tire when the calculated ratio Pk, Qk exceeds a preset threshold value Kp, Kq by multiple times successively.