In order to establish a national standard of laser energy for single laser pulses, we have developed a calibration system for laser energy meters used in industry. A reference calorimeter for measuring the absolute laser energy is composed of Bismuth Telluride semiconductor-based thermocouples and a high absorption optical cavity. To calibrate the sensitivity of devices under the test, we have adopted a simultaneous measurement method by splitting an optical laser pulse into two branches. Based on this measurement system, we will soon supply the energy standard.