A flow rate adjusting device includes a main body portion having a first opening portion to which a molten material is supplied, a second opening portion from which the molten material is discharged, a supply flow path communicating with the first opening portion and the second opening portion, and a cross hole intersecting the supply flow path; and a shaft-shaped valve portion disposed inside the cross hole. The valve portion has a tip end portion, a rear end portion, and a recessed portion provided between the tip end portion and the rear end portion and communicating with the first opening portion and the second opening portion, and the valve portion is rotated in the cross hole to change a position of the recessed portion, such that a flow path cross-sectional area of the supply flow path is changed to adjust a flow rate of the molten material discharged from the second opening portion; a storage chamber storing a part of the molten material flowing through the supply flow path between the first opening portion and the valve portion is defined by the tip end portion and an inner wall surface of the cross hole; the valve portion has a first contact surface provided between the recessed portion and the rear end portion and facing the rear end portion side; and the main body portion has a second contact surface to come into contact with the first contact surface from the tip end portion side.