A light guide device has a support member, a light guide member, a first abutting part, and a cover member. The light guide member is supported by the support member and has a light incident surface. The first abutting part has the light guide member and positions the light guide member at the first reference position predetermined in the support member by abutting on the abutted part of the support member. The cover member is attached to the support member and covers the light guide member. The cover member has a first biasing part that biases the light guide member in an abutting direction where the first abutting part abuts the abutting part, with the cover member attached to the support member, and an engaging part that engages with an engaged part of the support member while the first biasing part generates a biasing force in the abutting direction.