An ultrasound diagnosis apparatus and a 3-D image data scan method that can continuously display 3-D image data in both a pre-scan mode and a triggered entire volume mode by collecting the volume data of a plurality of volume scan regions of an object from the start of the scan. In the pre-scan mode, a plurality of 3-D sub-regions are set by dividing an object scan region along a direction vertical to the reference scan plane. In a triggered volume mode for collecting volume data, a 3-D scan of a 3-D sub-region including the reference scan plane is performed in preference to other 3-D sub-regions in order to continuously display 2-D image data acquired on the reference scan plane in the pre-scan mode and MPR image data acquired in the entire triggered volume mode from an initial scan time.