A current sensor includes a battery terminal portion that is conductive and is fastened to a battery post; a shunt resistor for current detection, which is formed in a plate shape and is electrically connected to the battery terminal portion; and a circuit board that is formed in a plate shape and is electrically connected to the shunt resistor, in which the shunt resistor is erected on a main surface of the circuit board. With this configuration, since the shunt resistor and the circuit board can be arranged so as not to face each other and not confront each other, the influence of heat generated by the shunt resistor can be suppressed.