Current sensor

A current sensor comprising:

• a current detection unit configured to detect a detection target current based on
• a terminal voltage of a shunt resistor located in series with a path through which the detection target current flows, and
• a detection resistance value being adopted for current detection and corresponding to a resistance value of the shunt resistor;
• a relay located in series with the path through which the detection target current flows;
• a relay control unit configured to turn on or off the relay;
• a resistance value correction circuit configured to
• calculate the resistance value of the shunt resistor as a calculated resistance value, and
• correct the detection resistance value based on the calculated resistance value;
• and
• a memory configured to store the detection resistance value, wherein
• the detection resistance value is originally stored in advance in the memory based on an initial resistance value of the shunt resistor,
• as the detection resistance value is corrected by the resistance value correction circuit, the detection resistance value as corrected is stored in the memory,
• the current detection unit is further configured to detect the detection target current while the relay is being turned on by the relay control unit, and
• the resistance value correction circuit is further configured to calculate the resistance value of the shunt resistor while the relay is being turned off by the relay control unit.