PURPOSE: To accurately detect an inclination of a tractor, etc. by a simple strucutre, by moving up and down a douser provided on a float which moves up and down in accordance with a liquid surface in a store case, betwen a light emission part and a photodetecting part, and cutting off or transmitting a light beam.

CONSTITUTION: Silicon oil or an antifreezing solution is put into a case 13A, and a float 14 which is spherical partially is floated so that its spherical surface 14a turs upward. ON the spherical surface 14a is provided a douser at 4 places of back and forth, and right and left, and at the position corresponding to the lower surface of a printed substrate 16 is provided a photosensor 17 consisting of a light emission part 17A and a photodetecting part 17B. On the upper part of the printed substrate 16 are installed electric parts 19, and a state of the photosensor 17 is outputted from a lead wire 20. The printed substrate 16 is placed between the case 13A and a cover 13B, and makes the case 13 airtight. In this case, an inclination of the case is detected by a pair of photodetecting states of back and forth, and right and left, of the photosensor 17. Also, since this device is an enclosed type, it is suitable for maintaining it horizontally, by loading it on various work devices to ground of a tractor, and adjusting an oil pressure cylinder by an output of the photosensor 17.