This signal processing device (110) is connected to an air bubble sensor (114) mounted on a tube through which a liquid flows, and is provided with: an interface unit (206) which acquires an air bubble signal obtained by receiving, through the tube, a signal sent in a direction perpendicular to the direction of flow of the liquid a tilt measurement unit (211) which, by incorporating an acceleration signal for each axis of the air bubble sensor (114), calculates the tilt angle of each axis of the air bubble sensor (114) and, on the basis of the calculated tilt angle on each axis, determines the mounting state of the air bubble sensor (114) relative to the tube and a signal processing unit (210) which calculates the size of the air bubbles by using pre-determined correction values according to the acquired air bubble signal and the determined mounting state.
