SENSOR INSERTION DEVICE

A sensor insertion device (44) comprises a main body case (45), a needle slider (52), a disposal slider (53), a spring (68), a puncture knob (46), and an opening mechanism (a window member (61) and a handle (63)). The needle slider (52) grips a needle (35) and a sensor (4) on a first end side, and is provided inside the main body case (45) in a state of being able to slide in the sensor insertion direction. The disposal slider (53) is provided inside the main body case (45) in a slidable state. The puncture knob (46) has an insertion hole (60) into which the rear end portion of the needle slider (52) can be inserted. The opening mechanism (the window member (61) and the handle (63)) puts the insertion hole (60) into a closed state when the needle slider (52) is being slid in the sensor insertion direction, and, put the insertion hole (60) in an open state in which the second end side of the needle slider (52) has been inserted into the insertion hole (60) by opening up the contact portion between the puncture knob (46) and the second end side of the needle slider (52) when the puncture operation is complete.