In this study, we propose a room-layout-based appliance control for voice user interfaces (VUIs), such as smart speakers. VUI-based appliance control requires a control command including which device to do what. However, we often experience an ambiguous target problem: the control target device in a control command is ambiguous because an ambiguous room name and demonstrative words are frequently used to specify the target device. To address this problem, we utilized a room layout to estimate the control target. A user implicitly aims to control devices in a room where they are. Therefore, we estimate the room where the user is now based on the room layout, which is estimated on a smart speaker, to determine the control target. In this study, we present the design of a room-layout estimator as the first step toward room-layout-based appliance control. The experimental evaluations conducted in our 1-bedroom smart house revealed that our room-layout estimator estimates room directions and room types with accuracies of 0.850 and 0.714, respectively.