To measure target component concentration in a liquid with higher accuracy without any dedicated apparatus or skill, a method is adapted to include: receiving a successive measurement value obtained by performing successive measurement of the target component concentration with use of a first measurement device immersed in the liquid; receiving a batch measurement value obtained by, with use of a second measurement device, performing batch measurement of the target component concentration in a part sampled from the liquid; and, when the batch measurement value is received, successively calculating a correlation value indicating the correlation between multiple successive measurement values and multiple batch measurement values respectively obtained in mutually corresponding multiple times of successive measurement and multiple times of batch measurement. In addition, the first measurement device is adapted to calculate the target component concentration or correct a successive measurement value with use of the latest correlation value.