The invention provides a control method and control device for an injection molding machine. A molding injection pressure Pi with which a parting opening Lm is formed between a movable mold 2m and a fixed mold 2c during injection-filling and which allows formation of a good molded article is obtained and set in advance. A molding clamping force Pc that allows formation of a good molded article is obtained and set in advance. During production, a mold clamping device Mc is clamped with the molding clamping force Pc, and an injection device Mi to apply the molding injection pressure Pi as a limit pressure Ps is driven to injection-fill a mold 2 with resin R. A parting opening detector 3 that detects the parting opening Lm is provided. During production, reset control is executed to reset the parting opening detector 3 to zero if reset timing tr set in advance has come at least on condition that given preparation for injection is completed after clamping. The reset timing is set in a range covering a given period Zs before injection start time and the given period Zs after the injection start time.