The capacity of installed photovoltaic (PV) generation in Japan has been expanding rapidly due to the governmental subsidy and feed-in tariff programs and then it has reached to 3.62 million kW as of 2010. This rapid increase in PV installation drives utilities to problems on how to operate stably the electric power systems. Therefore, electric power companies have to invest heavily in the systems. Our concern is to consider the possibility of implementing a demand response (DR) program as an alternative measure to the conventional power supply investment. This paper shows new findings from our simulations of voltage control by DR in distribution systems with high integration of rooftop PV. By our simulations based on the realistic input data, we clarified the economical efficiency of implementing the DR program as an alternative measure to the conventional investment in power supply against the voltage rise problem in distribution systems with PV.