An image recording apparatus, including: a platen which supports a sheet; a movable carriage disposed so as to face to the platen; a head mounted on the carriage to record an image on the sheet; an optical sensor mounted on the carriage and constituted by an emitting element which emits light and a receiving element which receives light reflected from the sheet and output an electric signal according to intensity of the reflected light; a changing mechanism which changes the optical sensor between first and second positions; and a calculation section which calculates at least one of a distance between the optical sensor and the sheet and a reflectivity of the sheet on the basis of (a) a first electric signal outputted from the receiving element with the optical sensor disposed at the first position and (b) a second electric signal outputted from the receiving element with the optical sensor disposed at the second position.