To provide an aerially installation type horizontal pump suitably usable in a required place for transferring fluid of a high head (pressure).

In this aerially installation type horizontal pump, impellers 14 and 16 are coaxially fixed to a horizontal rotary shaft 18 in two or more multistage shape, and a shaft seal device 34 is installed in an intermediate part of this horizontal rotary shaft 18. The impeller 16 arranged in the final impeller casing 12, and the impeller 14 arranged in an impeller casing 10 one before communicated with and connected to the final impeller casing 12 via a flow passage 24, are arranged back to back. A blade installing surface of the impeller 16 arranged in the final impeller casing 12, is opposed to the shaft seal device 34, and a suction port 30 is arranged on the shaft seal device 34 side.