An injection molding machine estimates a check valve wear amount, making it possible to predict a check valve use limit. At start of injection, the check valve is at a position advanced a stroke S0 with respect to a screw position (a position of a check seat that contacts the check valve and closes a resin flow channel). As the screw advances, the check valve retreats and closes when the screw moves a distance X0. When the check valve is worn ΔS (S1=S0+ΔS), it closes when the screw moves X1. Since the check valve stroke and the distance the screw moves until the check valve closes are proportional, S0/X0=S1/X1=a. Therefore, ΔS=aX1−S0, and the wear amount ΔS can be obtained by detecting the check valve closing position X1 and using this position X1 and the known stroke S0. The closing position is detected from the peak value of rotational force acting on the screw. Once the wear amount is obtained, the check valve use limit can be predicted from an allowable value of wear.