In a bus bar assembly includes a magnetic body having at least a first insertion hole and a second insertion hole and a bus bar. The bus bar is configured so that directions of electrical current flowing through it are opposed to each other at least once. The magnetic body includes a middle leg in the middle region located between portions of the bus bar. At least the middle leg defines a gap rendering a magnetic field discontinuous. The bus bar is configured to extend through the first insertion hole of the magnetic body from a first side of the magnetic body to a second side opposed to the first side with respect to an extending direction of the bus bar and further through the second insertion hole from the second side to the first side. The middle leg is located between the first and second insertion holes.