In software system testing using Bluetooth Low Energy (BLE), it is necessary to evaluate the system, including the wireless communication. However, it is difficult to build a test environment for testing with physical machines because of installation costs. This problem can be solved by emulation to reproduce BLE communication on computers; however, a BLE emulator is required. In this paper, we propose a BLE emulator called BluMoon for testing software systems using BLE. We impose the following requirements on the BLE emulator:(1) calculating the received signal strength for each frame and (2) imitating radio interference. To satisfy these requirements, we devised a software-implemented BLE controller with a host controller interface as a boundary and devised a data format called the BluMoon frame for sending and receiving data frame by frame. We designed and implemented BluMoon, and performed functional and performance evaluation as well as a comparative experiment with a physical environment. The results revealed that it is possible to implement a BLE emulator that meets the aforementioned requirements.