In recent years, MaaS (Mobility as a Service) concept has been attracting attention and expected to reduce transfer cost, that is one of the most crucial drawbacks of public transportation service. It is possible that transfer cost reduction will have a significant impact on the public transportation network and will require network modifications. This study applies an existing intercity multimode network optimization model to a suburban transportation system and presents a methodology to analyze the impact of transfer cost reduction on the optimal network and total regional consumer surplus. Through a simple example analysis, we show that not only transfer cost reduction but also appropriate network modifications are necessary to increase consumer surplus, and that transfer cost reduction does not simply imply either expansion or contraction of service area supplied by each transportation mode.