An indenter reference that is brought into contact with an axial second side surface of a sample which is arranged further toward an axial first side than an indenter, the indenter reference serving as a position reference for the indenter; a holder that detachably holds the indenter reference and is coupled with the indenter reference; an indenter position detector that couples with the holder and detects a relative position of the indenter with respect to the indenter reference; a regulator that allows displacement between a first position that regulates movement of the indenter reference with respect to the holder and a second position where the indenter reference can be removed from the holder; and a biasing portion that biases the regulator to be kept at the first position.