The present invention provides an insulating film for use in the motor of a refrigeration compressor using a substitute flon and a refrigerating machine oil in particular combination, which film is obtained by adding to a base film, or coating on the surface of a base film, a compound having at least one carbodiimide group, or, which film is made essentially of a compound having at least one carbodiimide group, represented by the following formula (1): ##STR1## or the following formula (2): ##STR2## or the following formula (3): ##STR3## or the following formula (4): ##STR4## This insulating film can eliminate the problems of the prior art, has excellent resistance to hydrolysis and forms no sludge, resultantly can prevent reduction in insulating property, and further has deterioration resistance to refrigerating machine oil.