An ultrasound diagnostic apparatus comprising: a display unit that displays a B-mode image in which at least a blood vessel region is imaged; a gate setting unit that sets a Doppler gate within the blood vessel region on the B-mode image, wherein the Doppler gate has an upper gate point (G1P) and a lower gate point (G2P) which face each other along a scan line passing through a center point of the Doppler gate; a blood vessel gradient acquisition unit that acquires a blood vessel gradient, the blood vessel gradient being an angle of the blood flow with respect to an horizontal line in the B-mode image; and characterised by: a vascular wall detection unit that detects an anterior vascular wall and a posterior vascular wall by performing image analysis on the B-mode image, on an outer side of the Doppler gate set by the gate setting unit in a direction perpendicular to the blood vessel gradient angle acquired by the blood vessel gradient angle acquisition unit; and the vascular wall detection unit has: an anterior wall detection unit that detects the anterior vascular wall in a range from an upper projection point obtained by projecting the upper gate point (G1P) on a blood flow perpendicular line that passes through the center point of the Doppler gate and extends perpendicular to the blood vessel gradient to a point positioned in a shallow portion direction apart from the upper projection point by a predetermined distance along the blood flow perpendicular line, and a posterior wall detection unit that detects the posterior vascular wall in a range from a lower projection point obtained by projecting the lower gate point (G2P) on the blood flow perpendicular line to a point positioned in a deep portion direction apart from the lower projection point by the predetermined distance along the blood flow perpendicular line. a display unit that displays a B-mode image in which at least a blood vessel region is imaged; a gate setting unit that sets a Doppler gate within the blood vessel region on the B-mode image, wherein the Doppler gate has an upper gate point (G1P) and a lower gate point (G2P) which face each other along a scan line passing through a center point of the Doppler gate; a blood vessel gradient acquisition unit that acquires a blood vessel gradient, the blood vessel gradient being an angle of the blood flow with respect to an horizontal line in the B-mode image; and characterised by: a vascular wall detection unit that detects an anterior vascular wall and a posterior vascular wall by performing image analysis on the B-mode image, on an outer side of the Doppler gate set by the gate setting unit in a direction perpendicular to the blood vessel gradient angle acquired by the blood vessel gradient angle acquisition unit; and the vascular wall detection unit has: an anterior wall detection unit that detects the anterior vascular wall in a range from an upper projection point obtained by projecting the upper gate point (G1P) on a blood flow perpendicular line that passes through the center point of the Doppler gate and extends perpendicular to the blood vessel gradient to a point positioned in a shallow portion direction apart from the upper projection point by a predetermined distance along the blood flow perpendicular line, and a posterior wall detection unit that detects the posterior vascular wall in a range from a lower projection point obtained by projecting the lower gate point (G2P) on the blood flow perpendicular line to a point positioned in a deep portion direction apart from the lower projection point by the predetermined distance along the blood flow perpendicular line. a vascular wall detection unit that detects an anterior vascular wall and a posterior vascular wall by performing image analysis on the B-mode image, on an outer side of the Doppler gate set by the gate setting unit in a direction perpendicular to the blood vessel gradient angle acquired by the blood vessel gradient angle acquisition unit; and the vascular wall detection unit has: an anterior wall detection unit that detects the anterior vascular wall in a range from an upper projection point obtained by projecting the upper gate point (G1P) on a blood flow perpendicular line that passes through the center point of the Doppler gate and extends perpendicular to the blood vessel gradient to a point positioned in a shallow portion direction apart from the upper projection point by a predetermined distance along the blood flow perpendicular line, and a posterior wall detection unit that detects the posterior vascular wall in a range from a lower projection point obtained by projecting the lower gate point (G2P) on the blood flow perpendicular line to a point positioned in a deep portion direction apart from the lower projection point by the predetermined distance along the blood flow perpendicular line. an anterior wall detection unit that detects the anterior vascular wall in a range from an upper projection point obtained by projecting the upper gate point (G1P) on a blood flow perpendicular line that passes through the center point of the Doppler gate and extends perpendicular to the blood vessel gradient to a point positioned in a shallow portion direction apart from the upper projection point by a predetermined distance along the blood flow perpendicular line, and a posterior wall detection unit that detects the posterior vascular wall in a range from a lower projection point obtained by projecting the lower gate point (G2P) on the blood flow perpendicular line to a point positioned in a deep portion direction apart from the lower projection point by the predetermined distance along the blood flow perpendicular line.