To provide a bubble detection system capable of recognizing a cause of generation of bubbles before the alarm is given based on a preset bubble alarm reference value if bubbles are mixed in a liquid passing through a conduit, especially, blood or transfusion solution, etc. passing through a conduit of a medical machine such as a blood circuit of a hemodialysis apparatus, a blood transfusion apparatus or an artificial cardiopulmonary apparatus, and adopting a means for improvement to prevent mixing of bubbles in the liquid passing through the conduit based on the recognized cause of generation of bubbles.

The bubble detection system is a system for detecting bubbles in the liquid passing through the conduit utilizing ultrasonic waves. The bubble detection system comprises a bubble detection means for detecting at least the number and the size (volume) of bubbles (single bubbles) passing through the conduit in the elapse of time, and a bubble integrating means for calculating the number and quantity of bubbles in the liquid passing through the conduit per fixed time by fixed size (volume) (by bubble diameter segment) in the elapse of time based on the result of detection of bubbles.