ROTATIONAL ANGLE DETECTING DEVICE

PROBLEM TO BE SOLVED: To provide a rotational angle detecting device for less input ports to a controller from the rotary encoder, which makes the controller smaller. SOLUTION: There are provided a rotary encoder 1 which, comprising a rotary plate 10, outputs a saw-tooth wave according to rotation of the rotary plate 10, a calculating part 5 for calculating rotational direction and rotational angle based on the output value of the rotary encoder 1, and a storage device 6 where a plurality of calculation results of the calculating part 5 are stored. The calculating part 5 classifies the magnitude of output value of the rotary encoder 1 at an arbitrary time into at least three layers, which are stored in the storage device 6. The magnitude of output value of the rotary encoder 1 at a time after a specified period since the arbitrary time is specified into at least three layers, and the rotational direction of the rotary encoder 1 is judged based on the layers at the arbitrary time and at the time after the specified period since then.