The inventive concept relates to a system supplying a constant current direct current power to serial loads connected in series with one another.The inventive concept is constituted by a constant current source power supply unit outputting a predetermined direct current, a load connection unit having the same rated current characteristic as the constant current source, a load connection unit having a rated current characteristic smaller than the constant current source, a load connection unit having a rated current characteristic greater than the constant current source, a load connection unit having a rated current characteristic greater or smaller than the constant current source and a circuit controlling or protecting them.