A sensor adhesion state determination system (100, 100a) comprising: a plurality of sensors (10-1~10-n, 10a-1~10a-n) adhered to a structure and configured to detect elastic waves; a calculator configured to calculate peak frequencies of the elastic waves on the basis of the elastic waves detected by the plurality of sensors; and a determiner (203, 203a) configured to determine an adhesion state of each of the plurality of sensors (10-1~10-n, 10a-1~10a-n) by comparing the peak frequencies with information serving as a determination reference, characterized in that the determiner is configured to calculate a count of elastic waves for a sensor, the count of elastic waves being the number of waves for which the difference between the calculated peak frequencies and resonant frequency of the sensor is less than or equal to a predetermined value, the determiner being configured to determine that the adhesion of the sensor (10-1~10-n, 10a-1~10a-n) to the structure is defective when the count of elastic waves is greater than or equal to a predetermined count, or, wherein each of the plurality of sensors (10-1~10-n, 10a-1~10a-n) has an oscillation function to oscillate at a specific frequency, and wherein the calculator is configured to calculate a peak frequency of an elastic wave generated by oscillation on the basis of the elastic wave output from a sensor that has detected the elastic wave, wherein the determiner is configured to determine that adhesion of an oscillating sensor is defective when some or all of the peak frequencies of the elastic waves are not within a range of peak frequencies serving as the determination reference. a plurality of sensors (10-1~10-n, 10a-1~10a-n) adhered to a structure and configured to detect elastic waves; a calculator configured to calculate peak frequencies of the elastic waves on the basis of the elastic waves detected by the plurality of sensors; and a determiner (203, 203a) configured to determine an adhesion state of each of the plurality of sensors (10-1~10-n, 10a-1~10a-n) by comparing the peak frequencies with information serving as a determination reference, characterized in that the determiner is configured to calculate a count of elastic waves for a sensor, the count of elastic waves being the number of waves for which the difference between the calculated peak frequencies and resonant frequency of the sensor is less than or equal to a predetermined value, the determiner being configured to determine that the adhesion of the sensor (10-1~10-n, 10a-1~10a-n) to the structure is defective when the count of elastic waves is greater than or equal to a predetermined count, or, wherein each of the plurality of sensors (10-1~10-n, 10a-1~10a-n) has an oscillation function to oscillate at a specific frequency, and wherein the calculator is configured to calculate a peak frequency of an elastic wave generated by oscillation on the basis of the elastic wave output from a sensor that has detected the elastic wave, wherein the determiner is configured to determine that adhesion of an oscillating sensor is defective when some or all of the peak frequencies of the elastic waves are not within a range of peak frequencies serving as the determination reference.