To provide a pump which can provide a stroke where at least rotation radius of an eccentrically rotating member is large.

This pump is equipped with a driving rotation shaft 30, an eccentric crank pin 38 which is eccentrically attached to the driving rotation shaft 30 and rotates eccentrically in relation to the driving rotation shaft 30, a reciprocating member including a piston 10 and a cam member 12 having a cam groove 12a engaging with the eccentric crank pin 38, a cylinder member 2 having a cylinder inner surface 25 suitable to the piston 10, and a fluid suction port 50 and a fluid delivery port 52 to a cavity formed by a cylinder member 2, a lid 6, and the piston 10. The cam groove 12a extends with 45 degrees diagonally to the reciprocating direction of the piston 10.