An intracerebral current simulation method including a first step of providing head image data; a second step of forming a three-dimensional brain model including micro-polyhedron units; a third step of providing first information which includes conditions under which a coil is placed on a patient's head, an electric current is applied to the coil, and the patient's reaction to the magnetic stimulation is observed, the conditions including a position and orientation of the coil, an electric current applied to the coil, and a structure relating to a generated magnetic field of the coil; and a fourth step of calculating an eddy current or electric field induced inside each of the micro-polyhedron units on the basis of the first information provided in the third step and second information which includes conductivity assigned to each micro-polyhedron unit. Also disclosed is a transcranial magnetic stimulation device and system.