To provide a circumference channel type underwater motor-driven pump for prevent fouling of the peripheral part of the pump by mud water, even at a low water level, when a pressure is bled during drive of the pump and cause effective functioning of cooling operation by pumping during a low water level.

The upper end of a tubular conduit 13, guided up along the inner surface of an oil chamber sidewall 14 from the terminal part 1e of the vortex of a vortex chamber 1, is guided to the lower end part of an annular channel 12. The upper end part of the annular channel 12 is continued to a pump discharge port. A lateral hole 18 is formed to radially extend from the hole peripheral part of a shaft hole 18 formed in the central part of a partition plate 9 to partition the vortex chamber 1 and an oil chamber 7 from each other. The upper end part of a vertical hole 15, formed in an under surface opening-form state along a vortex chamber sidewall 16, is continued to the terminal part of the lateral hole 17.