When a waveform monitor apparatus 1 of an injection molding machine M for monitoring an operation waveform at least during molding is configured by mounting the waveform monitor apparatus 1 on the injection molding machine M for performing molding according to a specific molding system, a parting opening detecting means Fp for detecting change data of a parting opening Lm to a time during molding, and an operation waveform displaying means Fd for displaying at least change data from a resin filling start is into a mold 2 to a cooling time termination to of the mold 2, detected by the parting opening detecting means Fp, on a waveform displaying portion 5 of a screen 4v on a display 4 attached to a molding machine controller 3 are provided.