This assistance device is provided with: a base； a torso support part provided with a base plate capable of supporting the torso of a person to be assisted, a sub-plate which has a lower bending rigidity than the base plate, is capable of being deformed by the body weight of the person to be assisted, and is capable of supporting the side of a lower part of the torso of the person to be assisted in comparison to the base plate, and a torso contact member which is more flexible than the sub-plate, and is provided to support surfaces of the base plate and the sub-plate at the side facing the person to be assisted, said torso support part being capable of relative movement with respect to the base while supporting the torso of the person to be assisted； and a drive unit which drives the torso support part.
