PURPOSE: To provide a simple and effective means for recovering rare metals contained in crude oil in the form of a porphyrin compound metal complex salt, by arraying plural permanent magnets to each outer wall of a rectangular main cylinder at a specific construction, attaching a blowdown valve to the cylinder and applying a magnetic field to the crude oil, etc.

CONSTITUTION: Plural permanent magnets 7, 7... are arranged at regular intervals alternately changing the direction of the pole on each outer wall 1a, 1b, 1c, 1d of a long rectangular main cylinder made of a metal such as stainless steel and having rectangular cross-section. The magnets 7 on the adjacent outer walls are detachably attached in a staggered manner. Blowdown valves 6, 6a are attached to the constricted parts of both ends of the rectangular main cylinder 1 through flanges 4. A crude oil containing rare metals as porphyrin compound metal complex salt is passed through the apparatus to effect the deposition of the rare metals together with the sludge on the inner wall of the main cylinder 1 and the rare metals are recovered therefrom.