An ultrasound diagnostic apparatus (1, 24) comprising: an ultrasound probe; an image acquiring unit configured to transmit an ultrasound beam from the ultrasound probe toward a subject and to receive the ultrasound beam in accordance with a first imaging condition to acquire an ultrasound image, wherein the first imaging condition includes a frame rate at the time of an ultrasound diagnosis, a resolution of the ultrasound image, brightness of the ultrasound image, and a dynamic range at the time of the ultrasound diagnosis; an orientation sensor configured to detect (i) an acceleration of three components along three axes that intersect with one another in a three dimensional space, (ii) an angular speed, in a case where the orientation sensor comprises a gyro sensor, or (iii) a position of the ultrasound probe; a probe orientation angle detecting unit configured to detect an orientation angle of the ultrasound probe on the basis of a signal of the orientation sensor; a part probability calculating unit (11, 25) configured to calculates, for the ultrasound image acquired in the image acquiring unit in accordance with the first imaging condition, a probability that a part of the subject included in the ultrasound image is a specific part on the basis of at least the orientation angle of the ultrasound probe detected by the probe orientation angle detecting unit; and an imaging condition changing unit configured to changes, when the probability calculated in the part probability calculating unit (11, 25) is greater than or equal to a predetermined threshold value, the first imaging condition to a second imaging condition for identifying the part for which the probability has been calculated, by changing at least one condition among the frame rate, the resolution, the brightness and the dynamic range of the first imaging condition, wherein the image acquiring unit is further configured to acquires an ultrasound image by using the second imaging condition. an ultrasound probe; an image acquiring unit configured to transmit an ultrasound beam from the ultrasound probe toward a subject and to receive the ultrasound beam in accordance with a first imaging condition to acquire an ultrasound image, wherein the first imaging condition includes a frame rate at the time of an ultrasound diagnosis, a resolution of the ultrasound image, brightness of the ultrasound image, and a dynamic range at the time of the ultrasound diagnosis; an orientation sensor configured to detect (i) an acceleration of three components along three axes that intersect with one another in a three dimensional space, (ii) an angular speed, in a case where the orientation sensor comprises a gyro sensor, or (iii) a position of the ultrasound probe; a probe orientation angle detecting unit configured to detect an orientation angle of the ultrasound probe on the basis of a signal of the orientation sensor; a part probability calculating unit (11, 25) configured to calculates, for the ultrasound image acquired in the image acquiring unit in accordance with the first imaging condition, a probability that a part of the subject included in the ultrasound image is a specific part on the basis of at least the orientation angle of the ultrasound probe detected by the probe orientation angle detecting unit; and an imaging condition changing unit configured to changes, when the probability calculated in the part probability calculating unit (11, 25) is greater than or equal to a predetermined threshold value, the first imaging condition to a second imaging condition for identifying the part for which the probability has been calculated, by changing at least one condition among the frame rate, the resolution, the brightness and the dynamic range of the first imaging condition, wherein the image acquiring unit is further configured to acquires an ultrasound image by using the second imaging condition.