Double container, method for attaching refill in double container, and connecting part

A double container, comprising:

• an inner container including a mouth part and a shoulder part;
• an outer container having a side wall, the outer container being configured to accommodate the inner container in a replaceable manner;
• a first connecting member having a two-stage tube shape, the first connecting member having an opening through which the mouth part of the inner container can be inserted, and the first connecting member being configured to be threadedly engaged with an outer surface of the side wall of the outer container while covering the shoulder part of the inner container and an upper end of the side wall;
• and
• a second connecting member having an approximately tube shape, the second connecting member having an opening through which the mouth part of the inner container can be inserted, and the second connecting member being situated on an inner side of the first connecting member,
• wherein the second connecting member comprises:
• an inner-circumference rotation restricting part configured to contact a part of the mouth part of the inner container to restrict rotation relative to the mouth part;
• and
• an outer-circumference rotation restricting part configured to contact a part of the side wall of the outer container to restrict rotation relative to the outer container, and
• in an assembled state, the inner container is restricted from rotation relative to the outer container.