A sensor insertion method for inserting a sensor into a user's body is provided. The method includes a unit fixing step of regulating a relative position between a sensor control unit and an inserting unit, where the sensor control unit is in a sensor insertion allowing state, and the inserting unit contains the sensor. In this step, the sensor control unit and the inserting unit are fixed to an insertion target portion of the user. Then, in a sensor inserting step, the inserting unit is caused to insert the sensor into the insertion target portion. In a sensor connecting step, the sensor control unit is shifted from the sensor insertion allowing state to a sensor connecting state, whereby electrical conduction is established between the sensor in the insertion target portion and the sensor control unit.
