To cope with the power shortage in Tohoku/Kanto district caused by the Great East Japan Earthquake on March 11, 2011, Article 27 of the Electricity Utility Industry Law came into force. The Article requires that large electricity users in Tohoku/Kanto district must cut power use during the summer by 15% from the maximum power consumption of the previous year. The Special Interest Group of Japan Telework Society on "Business Continuity and Telework" issued an urgent recommendation that the large electricity users should shut down the whole or part of the office buildings by allowing the employees to telework simultaneously in order to reduce a significant amount of power consumption. Not a few companies had attempted this approach. With the cooperation of the companies that implemented telework for the purpose of power-saving, this study verified the power-saving effects of the office-shutdown and evaluated a model of the electricity consumption in the office buildings. Based on the result of interviews and the numerical simulations, each company's efforts in reducing power consumption were classified and compared. This study identified various effects of the power-saving measures and revealed that simultaneous telework with office shutdown addressed in the recommendation is effective for a large scale power-saving.