Provided is a technology which improves reliability of the interaction between devices in a system where the devices communicate. In an information appliance system, multiple information appliances and a communication device such as a smart phone are in M2M communication. The communication device receives input of a voice from a user, and authenticates the user based on a voice signal, and sample voice data accumulated for user identification. The communication device performs a speech recognition process on the voice signal to determine an instruction of the user. When the user is authenticated and the instruction of the user is determined, the communication device transmits a command according to the instruction to an information appliance that is associated with the determined instruction of the user.