To compress an in-mold resin using the gate cutting function of an injection molding machine having the gate cutting function.

In the injection compression molding method of a synthetic resin product using the injection molding machine having the gate cutting function, a compression member 28 for compressing an in-mold synthetic resin is attached to a movable plate 27, to which the gate cutting pin in the injection molding machine is attached, in place of the gate cutting pin to compress the in-mold synthetic resin by the compression member 28. The compression member 28 is composed of compression pins concentrically arranged around a center pin 26 at an equal interval.