The authors propose an integrated approach to protocol specification design and a new method of synthesis of protocol specifications with more than one software module for the approach. In this approach, after designers specify protocols without any restrictions, errors included in the protocol specifications are automatically detected by the acyclic-expansion-based protocol validation and efficiently corrected by the component-based protocol synthesis. In the validation, incomplete specification parts consisting of executable state transition sequences to reach errors in each process are obtained. In the synthesis, the incomplete specification parts are completed by applying certain components which are provided as fundamental parts of correct specifications. The proposed approach has been implemented as an integrated system consisting of CAPE (computer-aided protocol engineering) tools for protocol validation and synthesis. The effectiveness of this approach has been confirmed experimentally. The proposed approach is expected to enhance the productivity of protocol specification design.>