A movement assistance apparatus to be provided in a movement assistance device and configured to execute a movement assistance operation for assisting movement of a user, the movement assistance apparatus comprising a mode switching control unit configured to switch, based on a magnitude of a surrounding risk on the movement of the user, a power mode between a normal mode in which the movement assistance operation is executable and a power saving mode in which a power consumption is smaller than a power consumption in the normal mode, wherein a condition for setting the power mode to the power saving mode includes a condition that the surrounding risk satisfies a predetermined low-risk condition, and a risk index acquisition unit (60; 60A; 60B; 60C) configured to acquire a risk index correlated to the magnitude of the surrounding risk on the movement of the user, wherein: the surrounding risk satisfies the predetermined low-risk condition when the risk index acquired by the risk index acquisition unit (60; 60A; 60B; 60C) is equal to or smaller than a predetermined threshold; and the surrounding risk is related to approaches of one or more vehicles (V; A; B; C) to the user; and the movement assistance apparatus being characterised in that: the risk index acquisition unit includes: one or more resonance devices (63a, 63b; 62, 65a, 65b) configured to resonate with sounds emitted by the one or more vehicles (V; A; B; C) approaching the user; one or more power generation devices (63a, 63c; 65a, 65b) configured to generate electric power along with resonances of the one or more resonance devices (63a, 63b; 62, 65a, 65b); and one or more detection devices configured to detect physical quantities related to power generations of the one or more power generation devices (63a, 63c; 65a, 65b); and the surrounding risk satisfies the predetermined low-risk condition when each of the physical quantities detected by the one or more detection devices is equal to or smaller than a predetermined threshold. the surrounding risk satisfies the predetermined low-risk condition when the risk index acquired by the risk index acquisition unit (60; 60A; 60B; 60C) is equal to or smaller than a predetermined threshold; and the surrounding risk is related to approaches of one or more vehicles (V; A; B; C) to the user; and the movement assistance apparatus being characterised in that: the risk index acquisition unit includes: one or more resonance devices (63a, 63b; 62, 65a, 65b) configured to resonate with sounds emitted by the one or more vehicles (V; A; B; C) approaching the user; one or more power generation devices (63a, 63c; 65a, 65b) configured to generate electric power along with resonances of the one or more resonance devices (63a, 63b; 62, 65a, 65b); and one or more detection devices configured to detect physical quantities related to power generations of the one or more power generation devices (63a, 63c; 65a, 65b); and the surrounding risk satisfies the predetermined low-risk condition when each of the physical quantities detected by the one or more detection devices is equal to or smaller than a predetermined threshold. the risk index acquisition unit includes: one or more resonance devices (63a, 63b; 62, 65a, 65b) configured to resonate with sounds emitted by the one or more vehicles (V; A; B; C) approaching the user; one or more power generation devices (63a, 63c; 65a, 65b) configured to generate electric power along with resonances of the one or more resonance devices (63a, 63b; 62, 65a, 65b); and one or more detection devices configured to detect physical quantities related to power generations of the one or more power generation devices (63a, 63c; 65a, 65b); and one or more resonance devices (63a, 63b; 62, 65a, 65b) configured to resonate with sounds emitted by the one or more vehicles (V; A; B; C) approaching the user; one or more power generation devices (63a, 63c; 65a, 65b) configured to generate electric power along with resonances of the one or more resonance devices (63a, 63b; 62, 65a, 65b); and one or more detection devices configured to detect physical quantities related to power generations of the one or more power generation devices (63a, 63c; 65a, 65b); and the surrounding risk satisfies the predetermined low-risk condition when each of the physical quantities detected by the one or more detection devices is equal to or smaller than a predetermined threshold.