A monitoring method for detecting terrain displacement, the method comprising: selecting an observation region using terrain model data including position information of a terrain; selecting an observation target within the observation region, whereby selecting an observation target optionally comprises selecting a target position at which a target is to be positioned using the terrain model data and delivering the target to the target position; specifying observation position coordinates of the observation region; installing a survey instrument having a distance measurement portion, an angle measurement portion (51, 52) and a photographic portion at a photographing position; determining coordinates of the photographing position of the survey instrument; photographing the observation region with a photographic portion of the survey instrument and observing the observation target at a first time point and a second time point, which is subsequent to the first time point, whereby through the photographing step, first and second photographs of the observation region at the first time point and the second time point are obtained and stored; and whereby through the observation step, distance measurement data measured by the distance measurement portion of the survey instrument and angle measurement data measured by the angle measurement portion (51, 52) of the survey instrument at the first time point and the second time point are obtained, to thus obtain first and second comparative observation data of the observation region including the distance measurement data, the angle measurement data and the observation position coordinates; and detecting displacement of the observation target target based on a comparison of the first and second image data and based on a comparison of the first and second comparative observation data. selecting an observation region using terrain model data including position information of a terrain; selecting an observation target within the observation region, whereby selecting an observation target optionally comprises selecting a target position at which a target is to be positioned using the terrain model data and delivering the target to the target position; specifying observation position coordinates of the observation region; installing a survey instrument having a distance measurement portion, an angle measurement portion (51, 52) and a photographic portion at a photographing position; determining coordinates of the photographing position of the survey instrument; photographing the observation region with a photographic portion of the survey instrument and observing the observation target at a first time point and a second time point, which is subsequent to the first time point, whereby through the photographing step, first and second photographs of the observation region at the first time point and the second time point are obtained and stored; and whereby through the observation step, distance measurement data measured by the distance measurement portion of the survey instrument and angle measurement data measured by the angle measurement portion (51, 52) of the survey instrument at the first time point and the second time point are obtained, to thus obtain first and second comparative observation data of the observation region including the distance measurement data, the angle measurement data and the observation position coordinates; and detecting displacement of the observation target target based on a comparison of the first and second image data and based on a comparison of the first and second comparative observation data.