An object is to reduce the axial dimension of an injection apparatus, melt a molding material uniformly, and improve the quality of molded products. A screw (20) comprises a plasticizing portion which comprises a body portion (45a) and a flight (53) projectingly formed on an outer circumferential surface of the body portion (45a). A groove-depth setting region is defined over a predetermined section of the plasticizing portion, and in the groove-depth setting region, the ratio γ1 of a groove depth τ1 to a diameter δ1 of pellets of a molding material falls within the range of 1≦γ1≦1.5 where the groove depth τ1 is a depth of a groove (67) formed along the flight (53). In the groove (67), pellets are arranged laterally and caused to advance while rolling along the groove (67). Since the pellets do not aggregate, no solid bed is formed.