An ultrasound imaging device, comprising: a data acquiring unit configured to acquire 3-dimensional ultrasound image data based on receive signals formed based on ultrasound echoes reflected from a target object; and a filtering unit configured to calculate a data acquisition ratio of amounts of the 3-dimensional ultrasound image data in predetermined data in an axial direction, a lateral direction and an elevation direction, and to determine a size of a filtering mask of an adaptive 3-dimensional filter in the axial direction, the lateral direction and the elevation direction according to the data acquisition ratio, characterized in that the filtering mask comprises a first filtering mask and a second filtering mask, wherein the filtering unit is configured to determine the second filtering mask to have a larger size than the first filtering mask and to filter the 3-dimensional ultrasound image data with the first filtering mask to thereby output first filtered ultrasound image data and to filter the 3-dimensional ultrasound image data with the second filtering mask to thereby output second filtered ultrasound image data; and in that the ultrasound imaging device further comprises: a scan converting unit configured to scan-convert the first and second filtered 3-dimensional ultrasound image data; a 3-dimensional rendering unit configured to perform 3-dimensional rendering upon the first and second scan-converted 3-dimensional ultrasound image data to form first and second 3-dimensional ultrasound images; a mixing unit configured to mix the first and second 3-dimensional ultrasound images to form a single 3-dimensional ultrasound image. a data acquiring unit configured to acquire 3-dimensional ultrasound image data based on receive signals formed based on ultrasound echoes reflected from a target object; and a filtering unit configured to calculate a data acquisition ratio of amounts of the 3-dimensional ultrasound image data in predetermined data in an axial direction, a lateral direction and an elevation direction, and to determine a size of a filtering mask of an adaptive 3-dimensional filter in the axial direction, the lateral direction and the elevation direction according to the data acquisition ratio, characterized in that the filtering mask comprises a first filtering mask and a second filtering mask, wherein the filtering unit is configured to determine the second filtering mask to have a larger size than the first filtering mask and to filter the 3-dimensional ultrasound image data with the first filtering mask to thereby output first filtered ultrasound image data and to filter the 3-dimensional ultrasound image data with the second filtering mask to thereby output second filtered ultrasound image data; and in that the ultrasound imaging device further comprises: a scan converting unit configured to scan-convert the first and second filtered 3-dimensional ultrasound image data; a 3-dimensional rendering unit configured to perform 3-dimensional rendering upon the first and second scan-converted 3-dimensional ultrasound image data to form first and second 3-dimensional ultrasound images; a mixing unit configured to mix the first and second 3-dimensional ultrasound images to form a single 3-dimensional ultrasound image. a scan converting unit configured to scan-convert the first and second filtered 3-dimensional ultrasound image data; a 3-dimensional rendering unit configured to perform 3-dimensional rendering upon the first and second scan-converted 3-dimensional ultrasound image data to form first and second 3-dimensional ultrasound images; a mixing unit configured to mix the first and second 3-dimensional ultrasound images to form a single 3-dimensional ultrasound image.