The liberalization movement in Japan will be expanded to the residential sector and full liberalization of the retail market will be achieved in the near future. Against this background, it is expected that transactions in a distribution network (DN), which has many consumers of the residential sector, will be activated. Furthermore, consumers can control their loads depending on the selling prices offered by retailers with the introduction of demand response (DR) technologies such as home energy management systems (HEMS). Due to the variation of load by DR, however, the voltage profile in DN may be changed compared to the present situation. This may make voltage management difficult and cause problems such as voltage deviation from an adequate range. In this paper, the impact of DR in a liberalized electricity market on DN is evaluated for efficient voltage management. In order to evaluate the behavior of the retailer and consumers, this paper proposes a bi-level programming approach based on the Stackelberg game model. Solving the bi-level programming problem including the power flow equation for a DN model based on the IEEE 13-bus test feeder, we analyze the impact of the retailer and consumers on the voltage in the DN in order to account for transactions between these market players.