When fuel passing through a fuel supply line and intake air passing through an air intake line are magnetically treated, magnetic reactions of the fuel and intake air are enhanced, and efficiency of the magnetic treatment is enhanced. A magnetic treatment apparatus for an engine which is provided in a fuel supply line and an air intake line of an engine, and performs magnetic treatment for fuel and intake air includes a magnet pair constituted of a pair of magnets opposed to each other with a pipe (the aforesaid fuel supply line and air intake line), and generating magnetic flux in a direction perpendicular to flows of the fuel and the intake air, and a casing covering the magnet pair, and has the constitution in which the casing accommodates a plurality of magnet pairs, and the magnet pairs are disposed along the pipe at predetermined spaces.