A seat sliding device comprising: a lower rail; an upper rail slidably provided on the lower rail and connected to a seat frame; a locking mechanism including a lock plate for locking the upper rail at a predetermined position of the lower rail, a locking spring member which biases the lock plate in a locking direction, and a release lever which operates the lock plate in an unlocking direction; and a slide lever for operation connected to a front end part of the release lever, characterized in that wherein the slide lever has a connecting end part in a tubular shape, and the front end part of the release lever is inserted in the connecting end part with a connection spring member therebetween, wherein the connection spring member is formed of a worked wire material for springs, is bent in the middle, and includes: a bent end located forward; two wire parts extending rearward from the bent end and biased in such a direction as to separate from each other; protruding engagement parts which are formed to protrude outward in the respective two wire parts at positions a predetermined distance apart from the bent end and, in a state in which the two wire parts are inserted in the front end part of the release lever, protrude outward from engagement protrusion holes formed in the front end part at opposed positions; and a front lock part provided on the bent end side and having an acting end biased in such a direction as to be apart from the two wire parts, and wherein the connecting end part of the slide lever has engagement holes formed at opposed positions, and is fitted on an outer side of the front end part of the release lever while the protruding engagement parts of the connection spring member protruding from the engagement protrusion holes of the front end part of the release lever engage with the engagement holes and an inner surface of the connecting end part is pressed by elastic force of the acting end of the front lock part of the connection spring member. a lower rail; an upper rail slidably provided on the lower rail and connected to a seat frame; a locking mechanism including a lock plate for locking the upper rail at a predetermined position of the lower rail, a locking spring member which biases the lock plate in a locking direction, and a release lever which operates the lock plate in an unlocking direction; and a slide lever for operation connected to a front end part of the release lever, characterized in that wherein the slide lever has a connecting end part in a tubular shape, and the front end part of the release lever is inserted in the connecting end part with a connection spring member therebetween, wherein the connection spring member is formed of a worked wire material for springs, is bent in the middle, and includes: a bent end located forward; two wire parts extending rearward from the bent end and biased in such a direction as to separate from each other; protruding engagement parts which are formed to protrude outward in the respective two wire parts at positions a predetermined distance apart from the bent end and, in a state in which the two wire parts are inserted in the front end part of the release lever, protrude outward from engagement protrusion holes formed in the front end part at opposed positions; and a front lock part provided on the bent end side and having an acting end biased in such a direction as to be apart from the two wire parts, and wherein the connecting end part of the slide lever has engagement holes formed at opposed positions, and is fitted on an outer side of the front end part of the release lever while the protruding engagement parts of the connection spring member protruding from the engagement protrusion holes of the front end part of the release lever engage with the engagement holes and an inner surface of the connecting end part is pressed by elastic force of the acting end of the front lock part of the connection spring member. a bent end located forward; two wire parts extending rearward from the bent end and biased in such a direction as to separate from each other; protruding engagement parts which are formed to protrude outward in the respective two wire parts at positions a predetermined distance apart from the bent end and, in a state in which the two wire parts are inserted in the front end part of the release lever, protrude outward from engagement protrusion holes formed in the front end part at opposed positions; and a front lock part provided on the bent end side and having an acting end biased in such a direction as to be apart from the two wire parts, and wherein the connecting end part of the slide lever has engagement holes formed at opposed positions, and is fitted on an outer side of the front end part of the release lever while the protruding engagement parts of the connection spring member protruding from the engagement protrusion holes of the front end part of the release lever engage with the engagement holes and an inner surface of the connecting end part is pressed by elastic force of the acting end of the front lock part of the connection spring member.