To enable high-speed printing even in an apparatus using a battery as a driving power source, by detecting a combination of groups making the number of drive times of a thermal head minimum on the basis of a dot count of each group and a count of dots that can be driven simultaneously, and driving the apparatus with the detected combination.

384 heat-generating resistors corresponding to 384 dots are divided to four groups of every 96 resistors. 96 heat-generating resistors can be driven simultaneously at most. First, it is checked whether or not a sum of dot counts n1, n2, n3, n4 included in dot patterns of characters is not larger than 96 (S110). When the sum is larger than 96, it is checked whether the minimum dot count n4 is larger than 96/2=48 or not (S130). If the dot count is larger than 48, dot patterns X1', X2', X3', X4' of characters having the dot counts n1, n2, n3, n4 respectively are driven separately (S140).