To provide an apparatus used for the purpose of energy saving, which serves as a brake by absorbing kinetic energy of a rotating body, and further has a structure for conserving the absorbed energy and discharging it at any time in the same direction as the time of absorption.

A set of planetary gear mechanisms is provided inside a case 1. A planetary gear 17 of the planetary gear mechanism performs only rotation when absorbing the energy, and performs only revolution about a main shaft 4 when discharging the energy. By this configuration, the rotational direction in discharging the energy becomes the same as the rotational direction in absorbing the energy. Further, energy conservation is carried out such that a spring 5 is deflected by the linear motion of a jam nut 6 caused by the rotation of a main shaft 4, which is also a shaft for a sun gear, having a partially threaded portion, and the absorbed energy by the spring 5 is conserved by a locking mechanism. When releasing the locking mechanism, the energy is discharged.