In order to provide a method and a device capable of precisely estimating a load acting on a tire with less sensors, a load estimation device 10 for estimating the load acting on the tire is provided with: an acceleration sensor 11; an acceleration waveform detection means 13 that detects an acceleration waveform in a tire radial direction on the basis of an output of the acceleration sensor 11; a differential acceleration waveform computing means 14 that differentiates the acceleration waveform to obtain a differential acceleration waveform; a peak position detection means 15 that detects a position of a peak on a leading edge side and a position of a peak on a trailing edge side appearing in the differential acceleration waveform; a ground contact time ratio calculation means 16 that calculates a ground contact time and a rotation time on the basis of the peak positions and calculates a ground contact time ratio, which is a ratio between the calculated ground contact time and the rotation time; and a load estimation means 19 that estimates the load acting on the tire on the basis of the calculated ground contact time ratio and a K-W map 18M representing a relationship between the calculated ground contact time ratio stored in a storage means 18 and the load.