PURPOSE: To improve rigidity of a core without deterioration in its magnetic characteristics by surrounding only the peripheral of a core leg constructed with amorphous magnetic alloy belts using a combination of two-divided reinforcing plates to make the section of the reinforcing plate polygonal.

CONSTITUTION: A core 4 having an octagonal section is formed with amorphous magnetic alloy belts. Two of the core 4 are arranged to combine those with reinforcing plates 5 (5A and 5B) obtained by two-dividing one sideleg of the two cores 4 in the widthwise direction. The core is constructed in such a manner that the section of the combined reinforcing plates 5 is made octagonal and a coupling portion of the plate 5 is overlapped on the core at the nearly central portion of the width of the core to construct the coupling portion of the reinforcing plates 5 so as to allow the both ends thereof to be engaged with each other in a slightly different form at each end. Thus, rigidity of the core 4 is improved without deterioration in its magnetic characteristics.