An injection molding apparatus is disclosed which includes a screw having a multichannel wave screw section. In the wave screw section, a helical passage defined by a radially extending helical screw flight is divided into a pair of flow channels by a radially extending helical barrier. The helical barrier is radially shorter than the helical conveying flight and the effective outer width thereof is axially narrower than the helical conveying flight. Each flow channel is provided with an undulating base surface that defines a plurality of wave cycles. The base surface varies in a radial direction between a valley portion and a crest portion for the wave cycle and a wave cycle is defined as extending between consecutive crest portions. The crest portions of one flow channel are helically displaced from the crest portions of the adjacent flow channel.