To provide a contents distribution system which protects copyright while securing user's convenience.

Contents 1 included in a data group 2 having a one-time password (contents authenticator) OTPk are executed by a specific control program and also executed by the specific control program according to a verification authenticator OTPk-1 generated from the contents authetnicator OTPk according to a unidirectional function; each time the contents are executed or as the time passes, information OTPk regarding a use frequency is updated and the contents authenticator and verification authenticator are varied while the relation by the unidirectional function is held. When information regarding the use frequency matches information found previously from a specified use frequency N, the execution of the contents by the control program is limited.