An injection unit comprising: a cylinder which heats a molding material; and a screw which is rotatably disposed in the cylinder, wherein the screw includes 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 screw has a first section where a depth of a groove formed by the flight is deep, a second section where the depth of the groove becomes shallower from the upstream side toward the downstream side, and a third section where the depth of the groove is shallow in this order from the upstream side to the downstream side, the flight includes 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 first flight portion is a same diameter flight portion having the same height from an upstream-side end portion of a top to a downstream-side end portion of the top, 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, the same diameter flight portion is provided at least in the first section, and the different diameter flight portion is not provided in the first section, and provided only in the third section or both in the second section and the third section. a cylinder which heats a molding material; and a screw which is rotatably disposed in the cylinder, wherein the screw includes 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 screw has a first section where a depth of a groove formed by the flight is deep, a second section where the depth of the groove becomes shallower from the upstream side toward the downstream side, and a third section where the depth of the groove is shallow in this order from the upstream side to the downstream side, the flight includes 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 first flight portion is a same diameter flight portion having the same height from an upstream-side end portion of a top to a downstream-side end portion of the top, 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, the same diameter flight portion is provided at least in the first section, and the different diameter flight portion is not provided in the first section, and provided only in the third section or both in the second section and the third section.