A linear measurement apparatus includes a measuring unit including at least one first noncontact distance measuring sensor and one second noncontact distance measuring sensor supported at a frame and aligned on opposite sides of a measured object. The measuring unit measures a plurality of first gap distances to a plurality of first object positions in a plurality of parallel first measurement lines and a plurality of second gap distances to a plurality of second object positions in a plurality of parallel second measurement lines. A distance calculator calculates a plurality of candidate object lengths on the basis of the first and second gap distances, each candidate object length being a distance between one of the first object positions and one of the second object positions. A maximum selector selects a maximum object length from among the plurality of candidate object lengths.