To provide an oil level detection device of an automatic transmission for adjusting oil level easily and accurately.

An oil level sensor 20 is installed in an oil pan 10 to form an inclination angle to a bottom surface. The oil level sensor 20 is composed of an oil level measuring tube 21, a conductive ball 24 which is accommodated in the oil level measuring tube 21 and vertically floats with following displacement of the oil level, a drive detection electrode 22 which comprises a pair of conductors oppositely disposed on an inner wall upper portion of one side of the oil level measuring tube 21 and a stop detection electrode 23 which comprises a pair of conductors oppositely disposed on other of inner wall upper portion.