In this paper, we discuss a service to give alarm in the case of emergency for the old and the weak by human behavior recognition in Intelligent Space. Our Intelligent Space consists of mobile robots, sensors and agents. Agent analyzes data acquired from networked devices and determines tasks of robot and space to provide a service for humans. In our emergency alarm service, human behavior recognition service module analyzes accelerometer data obtained from body-attached human behavior sensing platform, and classifies into four basic human behavior such as "walking", "running", "sitting" and "falling-down". For the old and the weak, "falling-down" behavior may bring about dangerous situations. On such an occasion, emergency alarm service is executed automatically and a selected mobile robot approaches fallen person quickly and then send images of the person to guardians. In this paper, we set up a scenario to verify the emergency alarm service in Intelligent Space, and show feasibility of the service from our simulation experiments.