Computing device, redundant system, program, and method for constructing redundant configuration

A computing device for configuring a redundant system includes: a detection unit configured to detect another computing device newly added to the redundant system during operation of the computing device; and a construction processing unit configured to execute construction processing for constructing a redundant configuration with the other computing device. The construction processing unit includes a first transmission unit for identifying construction start state information, and transmitting the construction start state information to the other computing device, and a second transmission unit for repeatedly performing identification of a change difference that arises in the state information as a result of computing processing of the computing device performed after identifying the construction start state information, from a time when the construction start state information was identified or a time when a previous timing was reached, and transmission of the change difference to the another computing device.