To provide a fluid mixing apparatus having high practical applicability and a high mixing efficiency even if the flow rate of a primary fluid fluctuates.

The fluid mixing apparatus comprises at least two primary fluid branch pipes 12 branched from a primary fluid flow path 11; a group of ejecters 3 connected to the primary fluid branch pipes; primary fluid valves 13 installed in front or rear of the respective ejecters of the group of the ejecters; secondary fluid branch pipes 14 branched from a secondary fluid flow path and connected to secondary fluid suction nozzles of the ejecters through secondary fluid valves 15; a primary fluid monitoring sensor 16 installed in the primary fluid flow path; and an automatic control means for adjusting at least one of the primary fluid valve, a secondary fluid adjustment means, and the secondary fluid valves based on the measurement value of the primary fluid monotiring sensor 16.