A slope monitoring system includes an analysis formula variable measuring means 81 which measures values of respective analysis formula variables that are obtained when a state of a test layer has been changed from a test environment in which there exist at least an arbitrary test layer or a test layer identical to a material layer forming a monitoring target slope, and a value of a predetermined first observable amount, and an analysis formula variable modeling means 831 which constructs, based on various values obtained from the test environment, for each of the analysis formula variables, a model defined a relationship of them with a second observable amount that is a predetermined observable amount being the same as the first observable amount, or having a known relationship with the first observable amount, or a predetermined third variable that can be calculated from the second observable amount.