An ultrasound system, comprising: an ultrasound data acquisition unit configured to transmit/receive ultrasound signals from/to a periodically moving target object to thereby form ultrasound data; and a processing unit coupled to the ultrasound data acquisition unit, wherein the processing unit comprises: a volume data forming section configured to form volume data including a plurality of frames based on the ultrasound data; a first image forming section configured to form a plurality of slice images based on the volume data; a period detecting section configured to set a feature point on each of the slice images based on brightness values of pixels included therein and form a feature point curve based on the feature points, the period detecting section being further configured to calculate zero crossing points in the gradient of the feature point curve and detect a period of the detected zero crossing points as a moving period of the target object, wherein the moving period comprises a plurality of local periods; a volume data reconstructing section configured to interpolate the volume data to have the same number of the frames within each local period and reconstruct the interpolated volume data into a plurality of sub-volume data, each sub-volume data is constructed by using frames at an identical position in each local period; a contour setting section configured to set contour of the target object on each of the sub-volume data; and a measuring section configured to measure the volume of the target object based on the contour to thereby form the volume information. an ultrasound data acquisition unit configured to transmit/receive ultrasound signals from/to a periodically moving target object to thereby form ultrasound data; and a processing unit coupled to the ultrasound data acquisition unit, wherein the processing unit comprises: a volume data forming section configured to form volume data including a plurality of frames based on the ultrasound data; a first image forming section configured to form a plurality of slice images based on the volume data; a period detecting section configured to set a feature point on each of the slice images based on brightness values of pixels included therein and form a feature point curve based on the feature points, the period detecting section being further configured to calculate zero crossing points in the gradient of the feature point curve and detect a period of the detected zero crossing points as a moving period of the target object, wherein the moving period comprises a plurality of local periods; a volume data reconstructing section configured to interpolate the volume data to have the same number of the frames within each local period and reconstruct the interpolated volume data into a plurality of sub-volume data, each sub-volume data is constructed by using frames at an identical position in each local period; a contour setting section configured to set contour of the target object on each of the sub-volume data; and a measuring section configured to measure the volume of the target object based on the contour to thereby form the volume information. a volume data forming section configured to form volume data including a plurality of frames based on the ultrasound data; a first image forming section configured to form a plurality of slice images based on the volume data; a period detecting section configured to set a feature point on each of the slice images based on brightness values of pixels included therein and form a feature point curve based on the feature points, the period detecting section being further configured to calculate zero crossing points in the gradient of the feature point curve and detect a period of the detected zero crossing points as a moving period of the target object, wherein the moving period comprises a plurality of local periods; a volume data reconstructing section configured to interpolate the volume data to have the same number of the frames within each local period and reconstruct the interpolated volume data into a plurality of sub-volume data, each sub-volume data is constructed by using frames at an identical position in each local period; a contour setting section configured to set contour of the target object on each of the sub-volume data; and a measuring section configured to measure the volume of the target object based on the contour to thereby form the volume information.