The focusing position detecting device includes contrast evaluation value calculating unit configured to calculate contrast evaluation values from a plurality of image data items obtained by imaging a subject a multiple number of times at a set exposure time while moving a focus lens in an optical axis direction within a search range, focusing position calculating unit configured to calculate a focusing position from focus positions at the time of imaging the subject a multiple number of times and the contrast evaluation values calculated by the contrast evaluation value calculating unit, detection unit configured to detect atmospheric fluctuation, and exposure time setting unit configured to set an exposure time in a case where the detection unit detects the atmospheric fluctuation so as to be longer than an exposure time in a case where the detection unit does not detect the atmospheric fluctuation.