Provided is a state detecting device capable of removing air bubbles existing inside effectively, no matter whether a liquid flow might be forward or backward. The state detecting device (1) detects the state of a liquid flowing in a pipe, while being interposed and arranged in the pipe. The state detecting device (1) comprises a liquid reserving portion (2) for reserving the liquid, an inlet portion (4) for letting the liquid in the liquid reserving portion (2), an outlet portion (5) for letting the liquid out the liquid reserving portion (2), an entrance (8) disposed on the upper side of the vertical central portion of the liquid reserving portion (2) mounted in the state detecting device (1) and forming the rear end portion of the inlet portion (4), and an exit (9) forming the front end portion of the outlet portion (5).
