A power system aggregation device comprising: a fitness evaluation function library configured to store two or more aggregation fitness evaluation functions (110a, 110b); and a processing unit configured to obtain an aggregation fitness from a detailed system model by using the aggregation fitness evaluation functions (110a, 110b) to create by a group creation an aggregation group from the aggregation fitness, and to create an aggregation system model from the aggregation group, wherein the processing unit is configured to calculate the aggregation fitness of two or more power system model constituent elements by using two or more fitness evaluation functions (110a, 110b) and to create the aggregation group on the basis of the aggregation fitness of the power system model constituent elements, wherein the processing unit is configured to perform model evaluation for evaluating at least one of analysis accuracy and a calculation amount of the aggregation system model, and wherein the power system aggregation device further comprises an aggregation log configured to store at least one of the model evaluation, the fitness evaluation functions (110a, 110b), the aggregation fitness, aggregation fitness evaluation parameters, the aggregation group, and a combined threshold of the aggregation group, characterized in that the group creation is configured to create an aggregation group consisting of a combination of elements of the power system model according to the obtained aggregation fitness and, as a process thereof, to calculate a similarity of two groups and to combine two groups whose similarity exceeds a threshold and is a maximum. a fitness evaluation function library configured to store two or more aggregation fitness evaluation functions (110a, 110b); and a processing unit configured to obtain an aggregation fitness from a detailed system model by using the aggregation fitness evaluation functions (110a, 110b) to create by a group creation an aggregation group from the aggregation fitness, and to create an aggregation system model from the aggregation group, wherein the processing unit is configured to calculate the aggregation fitness of two or more power system model constituent elements by using two or more fitness evaluation functions (110a, 110b) and to create the aggregation group on the basis of the aggregation fitness of the power system model constituent elements, wherein the processing unit is configured to perform model evaluation for evaluating at least one of analysis accuracy and a calculation amount of the aggregation system model, and wherein the power system aggregation device further comprises an aggregation log configured to store at least one of the model evaluation, the fitness evaluation functions (110a, 110b), the aggregation fitness, aggregation fitness evaluation parameters, the aggregation group, and a combined threshold of the aggregation group, characterized in that the group creation is configured to create an aggregation group consisting of a combination of elements of the power system model according to the obtained aggregation fitness and, as a process thereof, to calculate a similarity of two groups and to combine two groups whose similarity exceeds a threshold and is a maximum.