Tilt Detecting Device And Surveying Instrument

An inner frame is rotatably supported by the outer frame through a first shaft, a tilt detecting unit has a tilt sensor and is rotatably supported by the inner frame through a second shaft orthogonal to the first shaft, a first encoder is provided on the first shaft, a second encoder is provided on the second shaft, the tilt detecting device includes the motors provided on the respective shafts so that the respective shafts are rotated, and an arithmetic processing module which drives and controls the respective motors, in which the arithmetic processing module is configured to drive the respective motors so that the tilt sensor detects the horizontality based on a signal issued by the tilt sensor and to calculate a tilt of the outer frame based on the outputs from the first and second encoders when the tilt sensor detected the horizontality, and the arithmetic processing module is configured to reverse the tilt detecting unit 180° at least once based on the outputs from the respective encoders in relation to the first shaft and the second shaft in a stationary state of the tilt detecting device, and to perform the calibration of the tilt sensor based on the detection signals output from the tilt sensor before and after the reversal.