PURPOSE: To provide an encoder in which a reduction in a cost of a product, a light weight and a compact structure can be realized by simple means.

CONSTITUTION: An encoder has a light emitting element 3 and a light receiving element 4 oppositely disposed above and below a disc 11 to detect a rotating amount of the disc 11 upon reception of presence or absence or an emitted light L from the element 3, and comprises many microlenses 12 formed between the oppositely disposed elements 3 and 4 to convert the light L emitted from the element 3 toward the element 4 into parallel beam light L'. The microlens 12 is formed simultaneously by obtaining the disc 11 by molding a transparent material such as plastic, etc., by injection molding, etc., in a disc state.