The present invention provides a method of manufacturing a medical instrument provided with: a case which is formed by fitting a first case portion and a second case portion together, and which has an internal accommodating space； an elastic film made of an elastic member which is attached to the case and delimits a first accommodating space covered with the first case portion and a second accommodating space covered with the second case portion； a fixing portion which is formed at the periphery of each of the first case portion and the second case portion, and fixes the first case portion and the second case portion in a fitted state； a pinching surface which is formed at the periphery of each of the first case portion and the second case portion, and pinches the periphery of the elastic film； and a seal portion which is formed on the inside of the fixing portion at the periphery of the first case portion or the second case portion, and seals the elastic film, being pinched by the pinching surfaces, along the entire periphery thereof. The method of manufacturing a medical instrument is characterized in that, when the first case portion and the second case portion are assembled together by performing the fixing by means of the fixing portions and the sealing by means of the seal portion, an air gap formed between the fixing portions and the seal portion is decompressed or heated.La présente invention concerne un procédé de fabrication d'un instrument médical comprenant : un boîtier qui est formé en ajustant ensemble une première partie de boîtier et une seconde partie de boîtier, et qui a un espace de réception interne； un film élastique constitué d'un élément élastique qui est fixé au boîtier et délimite un premier espace de réception recouvert de la première partie de boîtier et un second espace de réception recouvert de la seconde partie de boîtier； une partie de fixation qui est formée à la périphérie de chacune de la première partie de boîtier et de la seconde
