a moving plate having a code pattern that is a position information code and is also an error determination code for an adjacent code;

an irradiator configured to irradiate the code pattern with light;

a light receiver configured to receive light emitted from the irradiator and passing through the code pattern; and

a determination part configured to specify an error portion occurring in a signal derived from the code pattern based on a relationship between a signal derived from the position information code and a signal derived from the error correction code, wherein:

the determination part includes an arithmetic processor configured to perform, when the position information code and the adjacent error correction code have a correspondence relationship, an arithmetic operation using the correspondence relationship, with the error correction code being added according to a code value of the arbitrary position information code in which the code patterns are consecutive, and

the determination part specifies the error portion based on a result of the arithmetic operation.