[Task] Provided is an injection unit in which whirling of a screw is suppressed and the friction between the screw and a cylinder is reduced. [Means for Resolution] An injection unit includes: a cylinder which heats a molding material; and a screw which is rotatably disposed in the cylinder, in which the screw has a rotary shaft, and a helical flight which protrudes from an outer periphery of the rotary shaft, and feeds the molding material from an upstream side to a downstream side along the rotary shaft by rotation of the rotary shaft, the flight has a helical first flight portion, and a helical second flight portion which is disposed on the further downstream side with respect to the first flight portion, the second flight portion is a different diameter flight portion in which a height of a downstream-side end portion of a top is lower than a height of an upstream-side end portion of the top, and the ratio of a flight width of the second flight portion to a pitch of the second flight portion is larger than the ratio of a flight width of the first flight portion to a pitch of the first flight portion.