To provide a reactor dispensing with a driving structure such as blade necessary for stirring, free from the fear of explosion or the like and also capable of dealing with slow cooling or heating.

This reactor 1 has as an essential element an upper reaction cylinder 2 constructed by providing metallic porous chambers 2A-2C formed by packing spherical metallic granulates in concentrically arranged metallic cylinders 5-7 and tightening and fixing the metallic cylinders with a gate G. Force feeding pipes 8P-10P are provided in one side of respective chamber 2A-2C and bottom plates are provided in another side. Penetrated holes 5a and 6a are drilled at the outer peripheral part of the small diameter cylinder 5 and the middle diameter cylinder 6 to move a fluid from the inside chamber 2A in the radial direction toward the outside chamber 2B and, on the other hand, a passage for cooling is formed on the outer periphery of the outermost chamber 2C and the outlet side of the upper reaction cylinder 2.