To diagnose soundness without being influenced by periodical fluctuation of an index itself for soundness diagnosis of a building, and to diagnose soundness stably by utilizing a deformation-load relation in a linear range.

This soundness diagnosis method based on microtremor measurement is executed as follows: measurement data of microtremors are collected by measuring regularly the microtremors of the building; measurement data of microtremors before and after the occurrence of a phenomenon which may exert an influence on the soundness of the building are extracted; measurement data of the microtremors before the occurrence of the phenomenon and after the occurrence of the phenomenon are divided plurally respectively; each index for diagnosing the soundness of the building is calculated relative to each piece of the divided measurement data of the microtremors; a regression line of the index before occurrence of the phenomenon and a regression line of the index after the occurrence of the phenomenon are estimated; and each intercept of the regression lines is compared each other, to thereby diagnose the soundness of the building.