To provide a monitoring system using one device available both as an at-home monitoring and a security monitoring through a remote operation from a portable terminal, which allows threshold settings for alarms and failure detection to be automatically performed to eliminate cumbersome procedures for a user.

An at-home monitoring mode or a security monitoring mode is specified for a monitoring server 6 from a portable terminal 7. An at-home abnormality or a security abnormality is determined from the number of detecting signals by a human body sensor 2 within a unit time for transmitting an alarm mail to the portable terminal. On the analogy of behavior patterns from statistical calculations of past data, the thresholds for alarm generation are automatically set up. In automatic detection of failure, data of connection abnormality between the human body sensor and a net top PC3 are transmitted to the monitoring server, so that a sensor abnormality mail is transmitted to the portable terminal. Conversely, in the case that the monitoring server receives no data within a specified time, a system failure downstream of the net top PC is determined, and a mail is transmitted to the portable terminal.