The invention discloses an automatic paper feeding device of a printer and an automatic paper feeding printer. The device comprises a first paper bin, a second paper bin, a first printing channel, a second printing channel, a paper feeding rubber roller, a paper feeding rubber roller position driving device, a paper feeding rubber roller rotary driving motor, a printing paper useup detector and a processor. The automatic paper feeding device of the printer is provided with two paper bins for supporting two printing rolled papers; when the printing rolled papers in one printing channel are used up, the paper feeding rubber roller approaches the other printing channel to convey the printing rolled papers in the other printing channel into the printing module of the printer to finish the process of automatically switching the printing rolled papers, so that no interruption of the printing work of the printer can be guaranteed all the time; and meanwhile, the printing rolled papers of the first paper bin and the second paper bin share one paper feeding rubber roller to finish switching of the printing rolled papers, so that the automatic paper feeding device of the printer is simple in structure, low in manufacturing cost and higher in economy.