To unify a fluid, shorten a mixing distance, reduce pressure loss, and promote mixing of the fluid by arranging a fluid mixer for turning a fluid around a flow passage, in a main pipe.

An upstream supplying pipe 3 is connected to a main pipe at an angle of 90 degrees, and a cross supplying pipe 4 is connected to the main pipe 1 and the supplying pipe 3 at an angle of 90 degrees in a position of a some downstream side. When a low temperature fluid is taken in from the supplying pipe 3, the pipe wall of the main pipe 1 is in a low temperature condition, and then, a high temperature fluid is taken in from the supplying pipe 4, and it is prevented heat stress from applying on the pipe wall of the main pipe 1. The high temperature fluid is taken in from the supplying pipe 4 in a condition crossed with the low temperature fluid from the supplying pipe 3, and is supplied to the downstream side from a fluid mixing pipe K in a condition of un-homogeneous fluid. A fluid mixer 2 is arranged between the supplying pipe 4 and an elbow 5 through the mixing pipe K, and a plurality of blades 21 twisted in one turning direction are arranged in a condition projected from the wall of the main pipe 1 toward a center. The unhomogeneous fluid is induced along the blades 21, and only homogeneous flow is supplied in the downstream of a mixing region.