A waveform measurement device includes an input spectrum acquisition unit for acquiring an input intensity spectrum being an intensity spectrum of pulsed light, an optical element inputting the pulsed light and outputting light having an intensity spectrum corresponding to a phase spectrum of the pulsed light, an output spectrum acquisition unit for acquiring an output intensity spectrum being an intensity spectrum of the light output from the optical element, and a phase spectrum determination unit for determining the phase spectrum of the pulsed light by comparing an output intensity spectrum calculated when the pulsed light having an input intensity spectrum and a virtual phase spectrum is assumed to be input to the optical element with the output intensity spectrum acquired in the output spectrum acquisition unit. The phase spectrum determination unit sets the virtual phase spectrum by deforming the control phase spectrum.