To provide an emergency drainage pump which can periodically be confirmed in its starting and operation conditions stably in air.

In an air-operable drainage pump, a mechanical seal 13 is connected to a cooler 14 by means of a lubricant passage. The lubricant for the mechanical seal 13 is circulated while being cooled by means of a seal ring having a lubricant circulating impeller. A rotating ring with cooling fins is arranged on a sliding part of the mechanical seal 13 for improving cooling effect of the mechanical seal 13. Sliding heat generated in air operation of the pump is diffused by a cooler and the cooling fin, for suppressing temperature rise of the mechanical seal 13 and thereby obtaining stable operation in air.