A pressure detection device of a liquid flow route, which detects a pressure of a liquid flow route consisting of a flexible tube, a portion of which is connected to a peristaltically-actuated tube that causes an internal liquid to flow by being compressed in a radial direction and being peristaltically actuated in a longitudinal direction in a peristaltic unit of a peristaltic pump (4, 4'), and which enables a predetermined liquid to be circulated comprising: a displacement detection device (18, 19, 25) that detects radial displacement of the peristaltically-actuated tube, wherein the peristaltic pump (4, 4') includes a gripping device (12, 12', 13) which grips the peristaltically-actuated tube attached to the peristaltic pump (4, 4'), and the displacement detection device (18, 19, 25) detects radial displacement of a portion gripped by the gripping device (12, 12', 13), wherein the gripping device (12, 12', 13) has a gripping piece (14, 16) which grips the peristaltically-actuated tube by radially pressing the peristaltically-actuated tube and a biasing device (15, 17) which biases the gripping piece (14, 16) against the peristaltically-actuated tube side, and wherein (i) the displacement detection device detects a load applied to a fixing end side of the biasing device and detects the radial displacement of the peristaltically-actuated tube based on the detected load, or (ii) the displacement detection device is arranged in a portion opposing the gripping piece (14, 16) by interposing the peristaltically-actuated tube therebetween, detects a pressure applied to a side surface of the peristaltically-actuated tube pressed by the gripping piece (14,16), and detects the radial displacement of the peristaltically-actuated tube based on the detected pressure, and characterized in that the biasing device is a torsion spring. a displacement detection device (18, 19, 25) that detects radial displacement of the peristaltically-actuated tube, wherein the peristaltic pump (4, 4') includes a gripping device (12, 12', 13) which grips the peristaltically-actuated tube attached to the peristaltic pump (4, 4'), and the displacement detection device (18, 19, 25) detects radial displacement of a portion gripped by the gripping device (12, 12', 13), wherein the gripping device (12, 12', 13) has a gripping piece (14, 16) which grips the peristaltically-actuated tube by radially pressing the peristaltically-actuated tube and a biasing device (15, 17) which biases the gripping piece (14, 16) against the peristaltically-actuated tube side, and wherein (i) the displacement detection device detects a load applied to a fixing end side of the biasing device and detects the radial displacement of the peristaltically-actuated tube based on the detected load, or (ii) the displacement detection device is arranged in a portion opposing the gripping piece (14, 16) by interposing the peristaltically-actuated tube therebetween, detects a pressure applied to a side surface of the peristaltically-actuated tube pressed by the gripping piece (14,16), and detects the radial displacement of the peristaltically-actuated tube based on the detected pressure, and characterized in that the biasing device is a torsion spring. (i) the displacement detection device detects a load applied to a fixing end side of the biasing device and detects the radial displacement of the peristaltically-actuated tube based on the detected load, or (ii) the displacement detection device is arranged in a portion opposing the gripping piece (14, 16) by interposing the peristaltically-actuated tube therebetween, detects a pressure applied to a side surface of the peristaltically-actuated tube pressed by the gripping piece (14,16), and detects the radial displacement of the peristaltically-actuated tube based on the detected pressure, and characterized in that the biasing device is a torsion spring.