A magnetic field generating-apparatus for biostimulation including: a C-shaped annular core having a gap-portion; and coils wound around the core, wherein the core includes a pair of facing extended-portions which lie on the both sides of the gap-portion and which face each other by extending toward the adjacent directions, and includes a pair of opposite-side portions which are juxtaposed on the respective outsides of the pair of facing extended-portions, and wherein the coils are wound around the pair of opposite-side portions respectively.