The invention discloses a needle bed device of a flat knitting machine and the flat knitting machine, and belongs to the technical field of flat knitting machines. The needle bed device comprises needle beds and inserting pieces, needle grooves are formed between the adjacent inserting pieces, lower knitting needles and lower needle jack pins are arranged in the needle grooves, conversion needle pins are arranged between the lower knitting needles and the lower needle jack pins, partition plates are further arranged in the needle grooves, upper knitting needles are arranged at the tops of thepartition plates, the rear ends of the upper knitting needles are connected with upper needle jack pins, push pieces are arranged at the bottoms of the upper needle jack pins, transition needle pins are arranged at the bottoms of the push pieces, the front ends of the conversion needle pins can be matched with the lower knitting needles or the transition needle pins, the lower needle jack pins candrive the lower knitting needles to move front and back through the conversion needle pins, and the lower needle jack pins can further drive the upper needle jack pins to swing upwards through the conversion needle pins, the transition needle pins and the push pieces. The number of the needle beds does not need to be increased, and assembly requirement of the needle bed device is reduced. The switching of the operation of the upper knitting needles and the lower knitting needles can be realized through the matching of the conversion needle pins, the transition needle pins and the push pieces,and the structure of the needle bed device is favorably simplified.