Digitization makes music, movies, and novels increasingly available to consumers. They also make information products more vulnerable to unauthorized use, and thus present a potent challenge to the copyright. Changing technology impels copyright holders to seek more protection from the law for their products. In an effort to retain control over distribution systems, industries that deliver copyrighted material join in those efforts. Information communication network such as Internet is the most important place in which crimes appear in number. On-line Service Providers(OSP) are regarded as having a substantial role to control and regulate the illegal behavior infringing of Copyright, so they should be liable to civil or criminal. The courts agreed the criminal responsibility of On-line Service Providers as assistance or aid. It expands criminal liability for infringing copyrights. This means OSP's liability is not regarded as principal offender in criminal. But they don't accept the opinion of applying exclusionary clause of Copyright Act. They want OSP to fulfill the highest level of technical filtering measures. Passive filtering measures cannot be the method of exemption from responsibility. It is very important to consider the principle of the legality of crimes and punishment. The strengthening the liability of OSP may bring about the chilling effect of freedom of speech and the use of Internet, and lead the conclusion of disregard of development of information technology and industry. OSPs have a duty of care to remove and manage the illegal contents on their service boards. But it is not consistently so. Duty of oversight and duty to care is restricted when they know the contents are obviously illegal and violate the copyright act. And the ability of OSP to control the contents according to technical or economical conditions also should be considered.