PURPOSE: To effectively bond a pair of cores by glass with high precision by forming a magnetic thin film on the upper face of a pair of magnetic blocks, then, processing to a I form and a C form and bonding both the cores by the glass.

CONSTITUTION: The 'Sendust(R)' thin film 3 is formed on the upper face of the blocks 2, 4 made of Mn.Zn ferrite according to a sputtering. The blocks 2, 4 are processed to form the C form core 2 and the I form core 4. After a low melting point glass 7 is placed on the gap opposing face of the cores 2, 4 fixed by a jig and heat-treated at about 600°C to bon. In this case, since a bonding glass 7 is melted while being brought into contact with the ferrite blocks 2, 4 good in a wettability, so that the gap part can be extremely effective ly bonded to effectively and highly precisely-bond a pair of cores by the glass.