A mount unit 10 is used for fixing, to a living body, a sensor 20 of which a portion 20a can be placed under the skin of the living body. The mount unit 10 includes a main body portion 11 that holds a placement of the portion of the sensor 20 under the skin of the living body and two or more holding portions 12a to 12d attached to the main body portion 11. Each of the holding portions 12a to 12d includes an adhesive material layer 13 capable of adhering to the living body and is movable so as to allow for selection between a state in which the adhesive material layer 13 is in contact with the living body and a state in which the adhesive material layer 13 is separate from the living body.
