In addition to puncture the skin of a subject, and a piston 40 that the puncture needle 30 having a capillary structure for collecting body fluids seeping from the skin is punctured is connected to the distal end, the puncture needle 30 can be fired in the puncture direction of the piston 40 at and has a first spring constant that is able to puncture the skin of a subject, and a spring 50 puncturing contact with the rear end of the piston 40, the second spring constant is smaller than the first spring constant It has, the spring 60 returns to rebound in the direction opposite to the puncture direction of the piston 40, and has a third spring constant is smaller than the first spring constant, and the by stretching in the puncture direction puncture button 80 which engages a stop spring 70 to stop the piston 40, the piston 40 is moved in the direction opposite to the puncture direction against the biasing force of the puncture spring 50, to fire the piston 40 by the opening operation , body fluid collecting device 1 with a housing 10 which houses the puncture button 80 spring 60, spring 70 and stop the piston 40, puncture spring 50, back. In the housing 10, the piston 40 is prevented from moving in the puncture direction from the predetermined position when stretched in the puncture spring 50, the locking portion 90 for restricting the movement of the piston 40 is provided. Puncture needle 30 pierces the skin of a subject by stretching of the puncture spring 50, is allowed to exit from the puncture site the puncture needle 30 by the rebound of the spring 60 to return the repulsive force of the spring 60 returns the pressing force of the stop spring 70 and is configured to be held at a position in contact with body fluids the tip of the puncture needle 30 by seeping bet is substantially balanced.被験者の皮膚を穿刺するとともに、穿刺された皮膚から湧出する体液を採取する毛細管構造を有する穿刺針30が先端に接続されたピストン40と、このピストン40を穿刺方向に発射して前記穿刺針30で被験者の皮膚を穿刺することが可能な第1バネ定数を有しており、当該ピストン40の後端と当接する穿刺バネ50と、第1バネ定数よりも小さい値である第2バネ定数を有しており
