To provide a muscular strength assisting device capable of being attached at the same time as the clothes are put on, and capable of concealing mechanical parts invisibly from the outside.

First-third arm members 3-5 and a driving control part 14 are attached to trousers 2, and first and second joint members 12 and 13, first-sixth belts 6-11, and first and second transmission wires 15 and 16 are assembled to the first-third arm members 3-5. Accordingly, a user can attach the first-third arm members 3-5 and the driving control part 14 to the body only by wearing the trousers 2, and can attach the mechanical parts such as the first and second joint members 12 and 13 and the first and second transmission wires 15 and 16 to the body at the same time. Furthermore, as the mechanical parts are covered with a cover member 30 openably/closably, the mechanical parts can be concealed invisibly from the outside, and therefore, the user can live daily life without feeling a sense of discomfort on the outside appearance.