An ultrasonic detection system calibration processing unit that performs calibration processing of an ultrasonic detection system having a transmitting element that transmits ultrasonic waves and a receiving element that receives reflected waves of the ultrasonic waves transmitted from the transmitting element and converts the reflected waves into reception signals corresponding to the intensity of the reflected waves and in which computational processing of distance information to a detection subject is performed using the reception signals, the ultrasonic detection system calibration processing unit comprising: distance information computing means that performs computational processing of the distance information using, among reception signal groups that are output, reception signals equal to or greater than a predetermined reference threshold value; calibration data acquiring means that acquires data of computational results of the distance information found using, among reception signal groups that are output in a state in which ultrasonic waves are being reflected by a predetermined detection subject, reception signals equal to or greater than a predetermined decision threshold value, with the calibration data acquiring means changing the decision threshold value and acquiring the data in regard to each of the decision threshold values; boundary value discriminating means that discriminates, from among the decision threshold values and on the basis of data groups of the computational results that have been acquired, a boundary value between a state in which the detection subject can be stably recognized and a state in which the detection subject cannot be stably recognized; and reference threshold value adjusting means that adjusts, on the basis of the boundary value that has been discriminated, the reference threshold value used when performing the computational processing of the distance information. characterized in that the ultrasonic detection system is an in-vehicle obstacle detection system, with at least the acquisition of the data by the calibration data acquiring means being executed in a state in which the vehicle is stopped. distance information computing means that performs computational processing of the distance information using, among reception signal groups that are output, reception signals equal to or greater than a predetermined reference threshold value; calibration data acquiring means that acquires data of computational results of the distance information found using, among reception signal groups that are output in a state in which ultrasonic waves are being reflected by a predetermined detection subject, reception signals equal to or greater than a predetermined decision threshold value, with the calibration data acquiring means changing the decision threshold value and acquiring the data in regard to each of the decision threshold values; boundary value discriminating means that discriminates, from among the decision threshold values and on the basis of data groups of the computational results that have been acquired, a boundary value between a state in which the detection subject can be stably recognized and a state in which the detection subject cannot be stably recognized; and reference threshold value adjusting means that adjusts, on the basis of the boundary value that has been discriminated, the reference threshold value used when performing the computational processing of the distance information. characterized in that the ultrasonic detection system is an in-vehicle obstacle detection system, with at least the acquisition of the data by the calibration data acquiring means being executed in a state in which the vehicle is stopped.