To solve a problem associated with formation of a transparent window portion in a biaxially stretch blow molded container by a nozzle structure of an injection molding apparatus, provided is a biaxially stretch blow molded container formed with a clearly transparent window portion in longitudinal strip shape by effectively preventing mixture of colored resin to window portion. Injection molding apparatus includes in nozzle portion a longitudinal groove flow path, wherein a transparent B resin flows. By, for example, reducing and increasing, respectively, the width and depth of the longitudinal groove flow path on the downstream side, and engraving slits in an inner mandrel and even in a front end portion of a stopper pin, flowability of the B resin in a horizontal direction is enhanced.