Abstract: An optical memory medium (2) has cores (21) each constituting a planar optical waveguide and clads (22) sandwiching each core, and has a data image (203) in which data is recorded as a scattering factor and a pair of positioning marks (201, 202) which are scattering factors required for positioning at an interface between a core (21) and a clad (22) or in the core (21). A read light (103) travels while spreading in the core (21) and scatters and interferes by the data image (203), and data is reproduced from a data reproduction light (1031) generated by this scattering and interference. A pair of positioning lights (101, 102) are caused to enter the core (21) with offsets with respect to the read light (103) in opposite directions along a thickness direction of the core (21), and scatter and interfere at the pair of positioning marks (201, 202).