To provide a water immersion detecting mechanism of a vertical submerged electrically driven pump in which a water immersion reservoir room having large interior capacity can be composed without heightening the whole height of a pump and even a float water immersion detecting sensor requiring a larger mounting space than an electrode type can be easily mounted in the water immersion reservoir room, and also, there is no more requirement to remove a pump casing and an oil casing even at the time of exchanging the water immersion detecting sensor due to failure and maintainability is excellent.

The water immersion reservoir room 9 having a watertight structure is attached to the outside of an oil chamber 1, and a ventilation passage 12 is opened by which an upper section in the water immersion reservoir room 8 and the inside of a motor chamber 13 are connected to each other, and also a water flow passage 13 is opened which is led from the periphery of a rotary shaft 4 in the oil chamber 1 to the inside of the water immersion reservoir room 8, and electrically connected so that energization to a motor can be shut off by receiving a water seepage detection signal outputted by water immersion into the water immersion reservoir room 8.