A pressure detection device of a liquid flow route that detects pressure of the liquid flow route configured 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 by being peristaltically actuated in a longitudinal direction by a peristalsis section of a peristaltic pump (4, 4'), and which enables a predetermined liquid to be circulated, characterized in that the pressure detection device comprises: - displacement detecting means (18, 30) that detects displacement of the peristaltically-actuated tube in the radial direction; - pressure calculating means that is able to calculate pressure of the liquid flow route based on the displacement of the peristaltically-actuated tube in the radial direction which is detected by the displacement detecting means (18, 30); and - calibration means that calibrates the displacement detecting means (18, 30) and the pressure calculating means, wherein the calibration means includes - closed flow route forming means (V1 to V9) that is able to form a flow route which is closed and includes a portion in the peristaltically-actuated tube at which the displacement detecting means (18, 30) is disposed, - pressure changing means that is able to arbitrarily change the pressure in the flow route formed and closed by the closed flow route forming means (V1 to V9), - pressure detection means that is able to detect pressure change in the flow route formed and closed by the closed flow route forming means (V1 to V9), and - calibration curve acquiring means that is able to produce and acquire a calibration curve with which the displacement detecting means (18, 30) and pressure calculating means are calibrated by a relationship between the pressure change detected by the pressure detection means when the pressure is changed by the pressure changing means and a detection value of the displacement detecting means (18, 30). - displacement detecting means (18, 30) that detects displacement of the peristaltically-actuated tube in the radial direction; - pressure calculating means that is able to calculate pressure of the liquid flow route based on the displacement of the peristaltically-actuated tube in the radial direction which is detected by the displacement detecting means (18, 30); and - calibration means that calibrates the displacement detecting means (18, 30) and the pressure calculating means, wherein the calibration means includes - closed flow route forming means (V1 to V9) that is able to form a flow route which is closed and includes a portion in the peristaltically-actuated tube at which the displacement detecting means (18, 30) is disposed, - pressure changing means that is able to arbitrarily change the pressure in the flow route formed and closed by the closed flow route forming means (V1 to V9), - pressure detection means that is able to detect pressure change in the flow route formed and closed by the closed flow route forming means (V1 to V9), and - calibration curve acquiring means that is able to produce and acquire a calibration curve with which the displacement detecting means (18, 30) and pressure calculating means are calibrated by a relationship between the pressure change detected by the pressure detection means when the pressure is changed by the pressure changing means and a detection value of the displacement detecting means (18, 30).