PROBLEM TO BE SOLVED: To provide a medical device capable of retaining a state where a needle part is punctured in a living tissue and enhancing safety by suppressing erroneous puncture, and a treatment method.SOLUTION: A medical device 1 for forming a hole at an oval fossa O in a living body, includes: a long needle part 30 provided with a puncture part 31 a tubular outer tube 60 for storing the needle part 30 an operating part 70 to which a proximal portion of the outer tube 60 is connected a move part 80 to which a proximal portion of the needle part 30 is connected and that is movable along the axial direction of the needle part 30 and a force generation part 90 applying force to the move part 80 in a direction of projecting of the puncture part 31 from the outer tube 60. The force generation part 90 can move the move part 80 to a distal side, where a distance between a proximal-side action part 121 and a distal-side action part 86 is longer than a natural length L0 of the force generation part 90.SELECTED DRAWING: Figure 2COPYRIGHT: (C)2018,JPO&INPIT【課題】生体組織に針部を穿刺した状態を維持でき、かつ針部による誤穿刺を抑制して安全性を高めることができる医療デバイスおよび処置方法を提供する。【解決手段】生体内の卵円窩Oに孔を形成するための医療デバイス1であって、穿刺部31が設けられる長尺な針部30と、針部30を収容する管状の外管60と、外管60の近位部が連結される操作部70と、針部30の近位部が連結され、針部30の軸方向に沿って移動可能な移動部80と、穿刺部31が外管60から突出する方向へ移動部80に力を作用させる力発生部90と、を有し、力発生部90は、移動部80を遠位側へ移動させることができ、近位側作用部121と遠位側作用部86の距離は、力発生部90の自然長L0よりも長い。【選択図】図2