A number of elderly people have a difficulty in going to the toilet by themselves. They sometimes wear an adult diaper but it makes the elderly uncomfortable and unsanitary. Moreover, their pride is injured by wearing the diaper. A portable toilet is also used for the elderly requiring assistance to the toilet. The portable toilet is not a sufficient solution because it is also uncomfortable and unsanitary for them. We propose a mobile toilet system for solving this problem. The concept of the proposed system is as follows. The toilet waits for calling signal from the elderly at standby room. When the calling signal is received, the toilet autonomously goes to the bedroom and approaches the elderly. After excreting, the toilet returns to the standby room and automatically disposes feces. In this paper, we present a prototype of the system and discuss the usefulness of the system.