An electric device for a human-powered vehicle comprises an accommodating structure. The accommodating structure includes a main body, an attachment member, and a power-supply accommodating part. The attachment member is configured to be attached to the main body. The power-supply accommodating part is provided at least one of the main body and the attachment member so as to accommodate a power supply, the power-supply accommodating part including an insertion opening and a first inner surface. The first inner surface extends along a reference plane and having a first outline defining a first area as viewed in a direction perpendicular to the reference plane. The insertion opening extends along an insertion opening plane non-parallel to the reference plane. The insertion opening has an opening outline defining an insertion opening area as viewed in a direction perpendicular to the insertion opening plane. The first area is larger than the insertion opening area.