To provide a pump driving device, having high versatility and realizing energy-saving and reduction of size by restraining extra pressure loss of a pump due to a flow change caused by configuration of a piping system and opening and closing of a valve.

This pump driving motor 6 includes a motor control circuit 7 adapted to control the pump pressure according to a flow rate on the basis of correlation (ω=ωO + coefficient A × motor current I) (wherein ωO is a motor basic rotational frequency) that when a flow rate of a fluid flowing through a pump chamber 2 changes, the rotational frequency of a rotary blade 3 body linearly changes depending on increase/decrease of a motor current.