Three point bending fatigue tests were carried out to investigate the influence of bias voltage on fatigue behavior of medium carbon steel with chromium nitride film. The substrate material of the specimens was JIS S45C medium carbon steel. The chromium nitride films were coated at two different bias voltages (VB = -20V, -300V) for fatigue test by arc ion plating method. As a result, the fatigue limit was improved by coating at low bias voltage, while the fatigue limit of high bias voltage samples decreased by coating. In order to clarify the difference between high and low bias voltages, the tensile test was performed using the coated specimens. For this test, the chromium nitride films were deposited at four different bias voltages. It was found the cracking behavior clearly changed between -40V and -80V. For low bias voltage samples, short cracks were initiated in the films, while the long cracks were initiated at same strain for high bias voltage samples. These differences between low and high bias voltage sample may be due to the elastic modulus of the film and droplets distribution in the film.