To provide an advanced standby operation pump improved so as to be capable of efficiently introducing air into a suction flow passage, by generating negative pressure in an opening part of a ventilation pipe in a suction casing, so as not to cause inconvenience such as intercepting a swirling flow in the suction casing and easily hitching on refuse.

This advanced standby operation pump includes the ventilation pipe 21 having one end opened in a peripheral wall pat 6A of a suction side casing 6 arranged on the upstream side in the fluid flowing direction of an impeller case 5 for storing an impeller 11 and having the other end opened in the atmosphere, and is provided with a vertical groove space part 29 continuing with an inside space 6S of the suction side casing 6 and projecting vertically or substantially vertically to the diametrical outside of a peripheral wall part 6A. One end opening part 25 of the ventilation pipe 21 is formed on an upstream side vertical sidewall 30 positioned on the upstream side in the impeller rotational direction among a wall for forming the vertical groove space part 29.