Abstract: A screw head device 1 for an injection molding machine includes a ring valve 3 set on a stem portion 2 of a screw head for movement in back and forth direction and for defining a rear side resin passage Rr between its own inner peripheral surface and the stem portion 2, a front side resin passage Rf extending axially and communicated with the rear side resin passage Rr, and a surge preventing mechanism, in which the front end of a screw main body Sm acts as a valve seat for mating with the rear end face of the ring valve 3. At a rear side of the head portion 4, a spacer guide 6 is provided. The outer peripheral surface 6s of the spacer guide 6 is located radially inside of the outer peripheral portion 4s of the head portions end racially outside of the bottom portion Rfd of the front side resin passage Rf.