To solve the problem that an ordinary gas alarm system is only to sound the alarm in the kitchen or the like where it is fixed, and therefore no alarm can be heard while people are out or away from it but at home.

After moving to a standby position by Step S440, this self-propelled vacuum cleaner determines whether or not there is any gas leakage from the sensing result by a gas sensor 82 at the standby position. If any gas leakage has occurred, it transmits to a specified receiver a text mail saying that a gas leakage has been sensed by Step S448. Then, it acquires a traveling route to a place specified as a first alarm position by Step S452 and Step S454. After arriving there through the traveling route by Step S456, it makes an alarm device 84 sound an alarm by Step S458. After a lapse of a prescribed time, it follows the similar processes by Step S462 through Step S466 to move to a place specified as a second alarm position, and continues to give the alarm. Afterwards, it keeps on going the round between the first alarm position and the second alarm position.