PURPOSE: To improve the efficiency of detection by inputting plural detection probability values from an input part without limiting the detection probability of a sensor to a specific value, and easily judging conditions such as the estimation of the position and presence range of a detected underwater body.

CONSTITUTION: A sensor ability calculation part 2 calculates the detecting ability value of the sensor 1 and a propagation state calculation part 3 calculates propagation loss corresponding to an underwater acoustic wave propagation distance. A detectable area calculation part 4 finds the detectable area of the underwater object by using the detecting ability value of the sensor 1 calculated by the calculation part 2 and the detection probability calculated by the calculation part 3. Plural detection probability values are inputted from the input part 5 without limiting the detection probability of the sensor 1 to the specific value and while the detecting ability value of the sensor 1 and propagation conditions, etc., are stored in a storage part 6, a detectable area corresponding to optional detection probability or detectable areas corresponding to the plural detection probability values are displayed on a display part 7 at the same time.