To produce low-cost high-quality modified water applicable to various uses at a low energy consumption in a short time by installing a mixing means for mixing water with a surfactant, a liquid transport means for causing a mixed fluid to flow, and a magnetic field application means for applying, to the fluid, a magnetic field in the direction crossing to the flow direction of the fluid.

In producing modified water by using a modified water production apparatus, when raw water to be treated is put in a water storage tank 1 and a circulation pump 2 is driven, the raw water flows through a minute eddy current generation apparatus 3 and a magnetic field application apparatus 4 and returns to the water storage tank 1. The magnetic field application apparatus 4 has a magnet arranged in the vicinity of a pipe forming a channel for the circulated water and generates such a magnetic field as to form lines of magnetic force in the direction crossing to the flow of the circulated water. When water passes through the magnetic field, a magnetic field is generated in the direction vertical to both the flow direction and the lines of magnetic force. Since water molecule clusters are electrified by this magnetic field and are given kinetic energy in the direction of this magnetic field, the collision among the water molecule clusters becomes violent, forming finer clusters.