PROBLEM TO BE SOLVED: To provide an extracorporeal circulation apparatus capable of highly accurately and easily detecting the volume of air bubbles using an ultrasonic signal detection part by saving time and labor of previously measuring and storing an air bubble amount and an air bubble measured value (waveform area) at the time of liquid flowing under various conditions.SOLUTION: An extracorporeal circulation apparatus 1 for circulating blood of a patient outside the patients body by using a circulation circuit includes a control part 10 which defines ultrasonic reception intensity acquired from an ultrasonic detection part 20 at the normal time in which air bubbles BL are not detected in the circulation circuit as a reference value, obtains the differences between the ultrasonic reception intensity and the reference value in a period during which the ultrasonic reception intensity acquired from the ultrasonic detection part attenuates from the reference value to a predetermined value or less, calculates an attenuation integrated value by integrating the differences, corrects the attenuation integrated value by using the reference value and normalizes it to estimate the size of the air bubbles.
