Provided is a puncturing instrument of novel structure, whereby exposure of the puncturing element in a lancet unit can be prevented, and an efficient puncturing operation by the puncturing element can be achieved. An elastic locking piece (122) that extends to the outside peripheral side is provided to the hub (116) of a lancet (14), and the elastic locking piece (122) is locked into a first locking hole (142) that opens onto the peripheral wall of a protector (112), whereby the hub (116) is retained in an initial position to the rear. The lancet (14) is mounted in a housing (16), whereby the release protrusion (30) of the housing (16) is inserted into the first locking hole (142), and the lock between the elastic locking piece (122) and the first locking hole (142) is released. A puncture-ready state is thereby brought about.
