To enhance prevention performance of deposition stuck to an inner wall surface of a tubular body and removal effect of the deposition stuck to the inner wall surface of the tubular body, to enhance prevention performance of corrosion on the inner wall surface of the tubular body, to remove affect to the environment and to reduce the cost by making the equipment in a small size and using an inexpensive treating accelerator and an inexpensive tubular body.

A coil 8 is disposed on the outside of the tubular body 6 forming a flow passage 4, and an electric current control means for electrifying an electric current having a specific wave form whose frequency varies time sequentially in a specific set band area is provided in the coil 8, and fluid in the flow passage 4 is treated by an electromagnetic field induced by the electric current flowing in the coil 8. In such the electromagnetic field treatment method of the fluid, a treating accelerator for accelerating treatment of the fluid by the electromagnetic field is added to the fluid in the flow passage 4.