A cutting mechanism (100) includes a receiving block (180), a cutting blade (275), a link member (220), and a cam portion (215). A tube is arranged on the receiving block (180). The link member (220) causes the cutting blade to move from a clamping position to a contact position by the link member (220) rotating from a clamping rotation position to a contact rotation position. The cam portion (215) causes the link member (220) to rotate from the clamping rotation position to the contact rotation position by the cam portion (215) rotating from a first intermediate rotation position to a first final rotation position. When the cam portion (215) rotates to the first intermediate rotation position, a pressing pin (215A) of the cam portion (215) presses a first arm portion (231) of a torsion spring (235) provided on the link member (220).