Replacement module capable of preventing foreign matter from entering when in attached state regardless of usage environment, electronic apparatus, and electronic apparatus set

A replacement module that is replaceably attached to an electronic apparatus, the replacement module comprising:

• an exterior portion that constitutes a part of an exterior of the electronic apparatus in an attached state of being attached to the electronic apparatus;
• a connection portion that is communicably connected to the electronic apparatus in the attached state;
• a holding portion that holds the attached state;
• and
• an entering preventing portion that has a ring shape, in which the connection portion and the holding portion are disposed inside, and is configured by an elastic body that prevents foreign matter from entering the connection portion and the holding portion in the attached state,
• wherein the connection portion, the holding portion, and the entering preventing portion are disposed in a common plane on a surface facing a side opposite to the exterior portion, and wherein the entering-preventing portion is configured, in the attached state, to be elastically deformed so as to make continuous surface contact with an abutting portion of the electronic apparatus over an entire circumferential range, thereby hermetically sealing the connection portion and the holding portion.