A sampler module is disclosed for use in a sampling waveform measurement device that samples subject signals and measures the waveform of the signals. The module is constructed by accommodating within a metal container: a laser diode driver circuit that receives laser drive sampling pulse signals from the outside and supplies pulse drive signals by a gain switching method, a laser diode that receives the drive signals from the LD driver circuit and generates optical probe pulse light, a sampling photoconductor that performs switching in accordance with irradiated light pulses and samples the subject signals, a condenser that focuses optical probe pulse light from the laser diode upon the photoconductor, and cooling temperature control means that maintains the temperature of the laser diode at a fixed temperature.