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.
