Disclosed herein is a detector that detects precision in charging current of a battery cell charging and discharging device, the detector including an instrument unit and a power supply unit, wherein the instrument unit includes a housing formed in a box shape open at a top thereof and a plurality of voltage measurement parts including a pair of connection terminals mounted at opposite sides of the housing inside the housing to detect precision in current of the charging and discharging device, the connection terminals being electrically connected to the power supply unit, and shunt resistance parts to apply uniform resistance to the respective connection terminals, and the power supply unit includes a charging and discharging device to supply current to the voltage measurement parts and to charge and discharge a battery cell and a multi-meter to measure current and voltage of the shunt resistance parts.