Prestressed cantilever comprising: a fixing module suitable for being fixed to a position on a base structure at which an extended structure is to be constructed; and a support structure, a portion of which is fixed to the fixing module, and which is suitable to support a bottom portion of a deck plate for traffic or pedestrians, the fixing module comprising: a pair of guide rails suitable for being provided on a side surface of the base structure, on which the extended structure is to be disposed, in a top-bottom direction while being spaced apart from each other at a predetermined distance; and a plate unit fitted to the guide rails and coupled to the support structure supporting the deck plate, wherein the plate unit comprises a support plate (121a, 121b) suitable for being fixed to the base structure and a movable plate movable along the guide rails in the top-bottom direction, wherein the support structure comprises a support frame fixed to the fixing module so as to be parallel to a flatland, with a top portion thereof suitable for being in contact with and supporting the deck plate, characterised in that the support structure further comprises a shaft arranged at a predetermined angle with respect to the support frame, with a first end of the shaft being connected to the fixing module and the other end at a point of a bottom portion of the support frame, wherein the first end of the shaft is connected to the movable plate such that a position at which the shaft is coupled to the fixing module is changed depending on movement of the movable plate in a top-bottom direction and; it further comprises a shock absorber provided between the movable plate and the shaft to absorb moment applied to the shaft. a fixing module suitable for being fixed to a position on a base structure at which an extended structure is to be constructed; and a support structure, a portion of which is fixed to the fixing module, and which is suitable to support a bottom portion of a deck plate for traffic or pedestrians, the fixing module comprising: a pair of guide rails suitable for being provided on a side surface of the base structure, on which the extended structure is to be disposed, in a top-bottom direction while being spaced apart from each other at a predetermined distance; and a plate unit fitted to the guide rails and coupled to the support structure supporting the deck plate, wherein the plate unit comprises a support plate (121a, 121b) suitable for being fixed to the base structure and a movable plate movable along the guide rails in the top-bottom direction, wherein the support structure comprises a support frame fixed to the fixing module so as to be parallel to a flatland, with a top portion thereof suitable for being in contact with and supporting the deck plate, characterised in that the support structure further comprises a shaft arranged at a predetermined angle with respect to the support frame, with a first end of the shaft being connected to the fixing module and the other end at a point of a bottom portion of the support frame, wherein the first end of the shaft is connected to the movable plate such that a position at which the shaft is coupled to the fixing module is changed depending on movement of the movable plate in a top-bottom direction and; it further comprises a shock absorber provided between the movable plate and the shaft to absorb moment applied to the shaft.