An encoder includes: a main scale having two or more band-shaped tracks in each of which an optical main grating is formed so that longitudinal direction of the main scale corresponds to a measurement axis direction; and an index scale opposed to the main scale so as to form a diffraction interference optical system in cooperation with the main grating, disposed so as to be movable relative to the main scale in the measurement axis direction, and in which two or more optical index gratings are formed. A plurality of slits included in the main grating in at least one track are formed so as to be inclined at a predetermined inclination angle from a direction perpendicular to the measurement axis direction so that pitch of the slits in the track becomes equal to the pitch of the slits in the at least one other track.