A waveform display device with a data management function acquires drive-axis data of a machine tool from a numerical controller for controlling the machine tool and acquires parameters of the numerical controller from the numerical controller. The waveform display device manages the drive-axis data and the parameters in association with each other, based on a time at which the drive-axis data is acquired and a time at which the parameter is acquired. These times of acquisition of the drive-axis data and the parameters are set by a timer of the waveform display device.