Method of purging for an injection molding machine

A method of purging for an injection molding machine employed for making a switch from a first molding material to a second molding material different from the first molding material by discharging a residue of the first molding material from an injection device and supplying the second molding material, the purging method comprising a switching purging step as a purging process step executed after the residual first molding material is discharged in advance from the injection device by a certain method, the switching purging step comprising a former purging step and a latter purging step executed after the former purging step, the former purging step including introduction of the second molding material into the injection device, and a metering operation and purging operation repeated a given number of times, the latter purging step including metering purging process and empty purging process performed a number of times corresponding to a given repeat count, the metering purging process including metering operation with a metering value smaller than that of the former purging step and purging operation repeated a given number of times, the empty purging process being performed after the metering purging process, the empty purging process including empty purging operation of making a screw retreat and then advance while the screw is not rotated, the empty purging operation being repeated a given number of times.