To provide a technique for automatically correcting cursors which do not fit in an ultrasonic image.

A reference cursor setting part 21 sets a reference cursor in a position where the thickness of an endothelium of a blood vessel is maximal. A measuring cursor setting part 22 sets a left side cursor in a position which is separated by L cm to the left from the reference cursor and a right side cursor in a position which is separated by L cm to the right from the reference cursor. A cursor determining part 23 determines whether the measuring cursors do not fit to a tomographic image of the blood vessel or not. When the left side cursor does not fit to the tomographic image, a cursor correcting part 24 sets a second right side cursor in a position which is separated by L cm to the right from the right side cursor instead of the left side cursor which does not fit. In addition, when the right side cursor does not fit, the cursor correcting part 24 sets a second left side cursor in a position which is separated by L cm to the left from the left side cursor instead of the right side cursor which does not fit.