A trouble processing method of ISDN communication system using an ISDN (Integrated Services Digital Network) and a control apparatus of ISDN communication system. Among a plurality of ISDN communication adapters included in an ISDN communication control apparatus, the same TEI (Terminal Endpoint Identifier) value as that of an active ISDN communication adapter is assigned to its stand-by ISDN communication adapter. The stand-by ISDN communication adapter is made to operate in the same manner as the active ISDN communication adapter with the exception of interruption of transmission of an LAPD (Link Access Producer on the D-channel) to an ISDN. The stand-by ISDN communication adapter is held in the same communication state as the active communication adapter. When a trouble has occurred in the active ISDN communication adapter, the interruption of transmission of the LAPD frame is cancelled and the stand-by ISDN communication adapter is activated as the active ISDN communication adapter. As a result, data communication using an ISDN can be conducted, and recovery processing at the time of occurrence of a trouble in an ISDN communication adapter can be rapidly executed without making the other party of communication conscious of it.