An assistance device includes: a base； a trunk support section including a base plate configured to support a trunk of a care receiver, a sub-plate, having a bending rigidity lower that of the base plate and deformable by the weight of the care receiver, which is configured to support, compared to the base plate, a lower portion of the trunk of the care receiver, and a trunk contact member, which is provided on a support surface on the side of the base plate and the sub-plate facing the care receiver, the trunk support section being configured to move relative to the base while supporting the trunk of the care receiver； and a driving section configured to drive the trunk support section.
