A protection control apparatus comprising a merging unit configured to merge system electric quantities detected in a power system, convert the system electric quantities into digital data, and output the digital data, the protection control apparatus protecting the power system, the protection control apparatus comprising: the merging unit including: a control-signal output circuit configured to generate a sampling signal in synchronization with a synchronization signal received from outside and output, as a control signal, numbers cyclically counted up every time the sampling signal is generated and the sampling signal; and a data output unit configured to convert the system electrical quantity into digital data based on the control signal output from the control-signal output circuit and output the digital data, characterised in that the control-signal output circuit includes: a number-of-clocks calculating circuit configured to calculate, based on its own clocks of the number-of-clocks calculating circuit, a first number of clocks in time from a minimum to a maximum of the numbers, a second number of clocks in a cycle of the synchronization signal, and a third number of clocks in time from detection of the synchronization signal until the sampling signal is generated; and a synchronization control unit configured to calculate a difference between the first number of clocks and the second number of clocks, control a cycle of the sampling signal based on the difference and the third number of clocks, and synchronize the generation timing of the sampling signal with the synchronization signal. the merging unit including: a control-signal output circuit configured to generate a sampling signal in synchronization with a synchronization signal received from outside and output, as a control signal, numbers cyclically counted up every time the sampling signal is generated and the sampling signal; and a data output unit configured to convert the system electrical quantity into digital data based on the control signal output from the control-signal output circuit and output the digital data, characterised in that a control-signal output circuit configured to generate a sampling signal in synchronization with a synchronization signal received from outside and output, as a control signal, numbers cyclically counted up every time the sampling signal is generated and the sampling signal; and a data output unit configured to convert the system electrical quantity into digital data based on the control signal output from the control-signal output circuit and output the digital data, characterised in that the control-signal output circuit includes: a number-of-clocks calculating circuit configured to calculate, based on its own clocks of the number-of-clocks calculating circuit, a first number of clocks in time from a minimum to a maximum of the numbers, a second number of clocks in a cycle of the synchronization signal, and a third number of clocks in time from detection of the synchronization signal until the sampling signal is generated; and a synchronization control unit configured to calculate a difference between the first number of clocks and the second number of clocks, control a cycle of the sampling signal based on the difference and the third number of clocks, and synchronize the generation timing of the sampling signal with the synchronization signal. a number-of-clocks calculating circuit configured to calculate, based on its own clocks of the number-of-clocks calculating circuit, a first number of clocks in time from a minimum to a maximum of the numbers, a second number of clocks in a cycle of the synchronization signal, and a third number of clocks in time from detection of the synchronization signal until the sampling signal is generated; and a synchronization control unit configured to calculate a difference between the first number of clocks and the second number of clocks, control a cycle of the sampling signal based on the difference and the third number of clocks, and synchronize the generation timing of the sampling signal with the synchronization signal.