A blood test device by which the amount of plumped skin at a puncture site for conducting a blood test or collecting blood can be controlled so that a blood component can be accurately measured. The blood test device includes: a housing an inner tube provided in one side of the housing a reciprocating unit which reciprocates within the inner tube a blood collection needle connected to the reciprocating unit a blood sensor facing to the blood collection needle and being located at the tip of the inner tube a measurement circuit to which a signal is fed from the blood sensor and a negative pressure unit driven by the measurement circuit. An outer tube, that is a tube covering the inner tube, has an opening in the tip side of the inner tube, is capable of moving relative to the inner tube, and is provided so as to return to a definite relative position. The negative pressure provider can apply a negative pressure to the inside of the outer tube.
