A state detecting device can efficiently remove air bubbles from a liquid no matter whether the liquid flows forwards or backwards. The state detecting device (1) is provided in a tube to detect a state of a liquid flowing in the tube. The state detecting device (1) includes: a liquid hold part (2) in which the liquid is stored； an inflow part (4) from which the liquid enters the liquid hold part (2)； an outflow part (5) from which the liquid exits from the liquid hold part (2)； an inlet (8) that is a rear end portion of the inflow part (4)； and an outlet (9) that is a front end portion of the outflow part (5). Here, the inlet (8) and the outlet (9) are arranged higher than a center of the liquid hold part (2) in a vertical direction when the state detecting device is provided in the tube.
