An encoder device includes a first array that includes first through fourth photodiodes adjacent to each other in an X direction, each having a length of X1; a second array that includes fifth through eighth photodiodes adjacent to each other in the X direction, each having a length of X1, and is adjacent to the first array in a Y direction but displaced by X1/2 in the X direction relative to the first array; a slit member that includes light transmitting sections and light shielding section arranged alternately, each having a length 2×X1, and is movable in the X direction; and a logic circuit that generates first and second detection signals from output signals of the first through fourth photodiodes and output signals of the fifth through eighth photodiodes, respectively, a phase of the second detection signal being shifted by a ¼ period of the first detection signal relative to the first detection signal.