A banknote size adjustment device, configured to be arranged in a banknote box, the banknote size adjustment comprising: a pair of assemblies cooperating with each other to form a space for accommodating banknotes, a size of the space for accommodating banknotes being adjustable; and a front support frame and a rear support frame, wherein corresponding transverse scales and corresponding longitudinal scales are provided on the front support frame and the rear support frame, and a plurality of positioning holes corresponding to the transverse scales and the longitudinal scales are provided in the front support frame and the rear support frame, the front support frame and the rear support frame are configured to be fixed to an inner front wall and an inner rear wall of the banknote box respectively and configured to support the pair of assemblies; wherein each of the assemblies comprises a position-limiting plate, a reinforcing plate, a pair of latch plates and a pair of compression springs, the reinforcing plate is fixed to a bottom of the position-limiting plate, and one of the latch plates is arranged at one end of the position-limiting plate and the reinforcing plate and is sandwiched between the position-limiting plate and the reinforcing plate, one of the compression springs has one end fixed to the reinforcing plate or the position-limiting plate and another end connected to one end of the one of the latch plates, and is configured to apply an elastic force to the one of the latch plates, to allow another end of the one of the latch plates to always maintain a tendency of being inserted into the positioning holes, and the other one of the latch plates is arranged at another end of the position-limiting plate and the reinforcing plate symmetrically with respect to the one of the latch plates, and the other one of the compression springs is arranged at the another end of the position-limiting plate and the reinforcing plate symmetrically with respect to the one of the compression springs, and the assembly is positioned on the front support frame and the rear support frame by the pair of latch plates. a pair of assemblies cooperating with each other to form a space for accommodating banknotes, a size of the space for accommodating banknotes being adjustable; and a front support frame and a rear support frame, wherein corresponding transverse scales and corresponding longitudinal scales are provided on the front support frame and the rear support frame, and a plurality of positioning holes corresponding to the transverse scales and the longitudinal scales are provided in the front support frame and the rear support frame, the front support frame and the rear support frame are configured to be fixed to an inner front wall and an inner rear wall of the banknote box respectively and configured to support the pair of assemblies; wherein each of the assemblies comprises a position-limiting plate, a reinforcing plate, a pair of latch plates and a pair of compression springs, the reinforcing plate is fixed to a bottom of the position-limiting plate, and one of the latch plates is arranged at one end of the position-limiting plate and the reinforcing plate and is sandwiched between the position-limiting plate and the reinforcing plate, one of the compression springs has one end fixed to the reinforcing plate or the position-limiting plate and another end connected to one end of the one of the latch plates, and is configured to apply an elastic force to the one of the latch plates, to allow another end of the one of the latch plates to always maintain a tendency of being inserted into the positioning holes, and the other one of the latch plates is arranged at another end of the position-limiting plate and the reinforcing plate symmetrically with respect to the one of the latch plates, and the other one of the compression springs is arranged at the another end of the position-limiting plate and the reinforcing plate symmetrically with respect to the one of the compression springs, and the assembly is positioned on the front support frame and the rear support frame by the pair of latch plates.