An ultrasonic imaging system, comprising: an ultrasonic probe unit that is configured to transmit an ultrasonic wave to a surface of a sample and receive a reflected wave from the surface of the sample; a position control device; and a control device; wherein the position control device, comprises: a storage unit configured to store a deviation between the time from transmitting an ultrasonic wave from the ultrasonic probe unit to the sample until a reflected wave is received and a reference time, the reference time being the time from transmitting the ultrasonic wave until the reflected wave is received when the distance between the ultrasonic probe unit and the surface of the sample is equal to the focal distance of the ultrasonic probe unit; a processing unit configured to determine a position of the ultrasonic probe unit in a direction perpendicular to the surface of the sample and to calculate a deviation between the time from transmitting an ultrasonic wave until a reflected wave is received and the reference time; wherein the storage unit is configured to store the deviation in an (n-1)-th line as previously calculated by the processing unit when the ultrasonic probe unit scans the (n-1)-th line of a surface of a sample in a first surface direction of the sample before the ultrasonic probe unit moves by a predetermined pitch in a second surface direction perpendicular to the first surface direction in order to scan an n-th line of the surface of the sample in the surface direction opposite to the first surface direction; and wherein the processing unit is configured to determine the position of the ultrasonic probe unit in the direction perpendicular to the surface of the sample when the ultrasonic probe unit scans the n-th line of the surface of the sample based on the deviation in the (n-1)-th line stored in the storage unit, wherein the control device is configured to control the position of the ultrasonic probe unit in a direction perpendicular to the surface of the sample to the position determined by the position control device when the ultrasonic probe unit scans the n-th line of the surface of the sample; and wherein the processing unit is configured to to calculate a deviation in the n-th line between the time from transmitting an ultrasonic wave until a reflected wave is received and the reference time when the ultrasonic probe unit scans the n-th line of the surface of the sample, and to store the calculated deviation in the storage unit. an ultrasonic probe unit that is configured to transmit an ultrasonic wave to a surface of a sample and receive a reflected wave from the surface of the sample; a position control device; and a control device; wherein the position control device, comprises: a storage unit configured to store a deviation between the time from transmitting an ultrasonic wave from the ultrasonic probe unit to the sample until a reflected wave is received and a reference time, the reference time being the time from transmitting the ultrasonic wave until the reflected wave is received when the distance between the ultrasonic probe unit and the surface of the sample is equal to the focal distance of the ultrasonic probe unit; a processing unit configured to determine a position of the ultrasonic probe unit in a direction perpendicular to the surface of the sample and to calculate a deviation between the time from transmitting an ultrasonic wave until a reflected wave is received and the reference time; a storage unit configured to store a deviation between the time from transmitting an ultrasonic wave from the ultrasonic probe unit to the sample until a reflected wave is received and a reference time, the reference time being the time from transmitting the ultrasonic wave until the reflected wave is received when the distance between the ultrasonic probe unit and the surface of the sample is equal to the focal distance of the ultrasonic probe unit; a processing unit configured to determine a position of the ultrasonic probe unit in a direction perpendicular to the surface of the sample and to calculate a deviation between the time from transmitting an ultrasonic wave until a reflected wave is received and the reference time; wherein the storage unit is configured to store the deviation in an (n-1)-th line as previously calculated by the processing unit when the ultrasonic probe unit scans the (n-1)-th line of a surface of a sample in a first surface direction of the sample before the ultrasonic probe unit moves by a predetermined pitch in a second surface direction perpendicular to the first surface direction in order to scan an n-th line of the surface of the sample in the surface direction opposite to the first surface direction; and wherein the processing unit is configured to determine the position of the ultrasonic probe unit in the direction perpendicular to the surface of the sample when the ultrasonic probe unit scans the n-th line of the surface of the sample based on the deviation in the (n-1)-th line stored in the storage unit, wherein the control device is configured to control the position of the ultrasonic probe unit in a direction perpendicular to the surface of the sample to the position determined by the position control device when the ultrasonic probe unit scans the n-th line of the surface of the sample; and wherein the processing unit is configured to to calculate a deviation in the n-th line between the time from transmitting an ultrasonic wave until a reflected wave is received and the reference time when the ultrasonic probe unit scans the n-th line of the surface of the sample, and to store the calculated deviation in the storage unit.