Abstract: An alarm device adapted particularly for the indication of electrical leakage and mal-insulation of electrical appliances disposed in association with a marine tank for use in fish raising. An electrical leakage sensor unit is provided in the tank, to which are electrically plugged the illumination light, air pump, temperature controller, water filter member, germicidal light, so that an alarm signal led via an IC comparator and further to a sonic frequency vibrator for transformation and further to an signal amplifier and subsequently to a parallelly-connected buzzer and red-light indicator to simultaneously alarm the operator of the hazard of electrical leakage and mal-insulation.