A pressure detection device of a liquid flow route is provided which detects a pressure of an arterial blood circuit consisting of a flexible tube, a portion of which is connected to a peristaitically-actuated tube that can cause an internal liquid to flow by being compressed in a radial direction and being peristaltically actuated in a longitudinal direction in a roller of a blood pump, and which enables a predetermined liquid to be circulated. The pressure detection device includes a load sensor that detects radial displacement of the peristaltically-actuated tube.