a printing device having a plurality of print hammers having striking surfaces arranged along a print line and print magnets provided adjacent to one another for driving the printing hammers . a magnetic interference preventing device comprises a memory for storing for each column the excitation lapse time information of the print magnets . a reader which , when exciting each print magnet is started , reads the excitation lapse time information of both print magnets adjacent to each print magnet out of the memory . the reader outputs a signal only when the excitation lapse times of both print magnets are in a predetermined range of time . an inhibitor is used for inhibiting the excitation of each print magnet when the excitation lapse times of both print magnets are within the predetermined range of time .