PROBLEM TO BE SOLVED: To provide a multi-leaf collimator and a charged particle ray treatment device, capable of improving position precision of a leaf plate.SOLUTION: A multi-leaf collimator 10 forming an opening T through which charged particle ray R passes includes: a plurality of leaf plates 20 provided side by side in a specified parallel direction orthogonal to an irradiation axis A of the charged particle ray R a motor 30 which is attached to the base end part 20a side of the leaf plate 20 for reciprocating the leaf plate 20 fixing rollers 40, 41 and support rollers 50, 51 which are provided so as to pinch the tip end part 20a side of the leaf plate 20 in an extension direction of the irradiation axis A, for supporting the leaf plate 20 for free reciprocation and an elastic force apply part which applies an elastic force toward the leaf plate 20 to the support rollers 50, 51.
