PURPOSE: To provide a printer in which the efficiency of a transfer process can be enhanced.

CONSTITUTION: The printer comprises an array having a plurality of elements, a driver 36 arranged corresponding to the array, a latch circuit 35 arranged corresponding to the driver 36 to hold dot line data, and a shift register 33 arranged corresponding to the circuit 35 to output the data. The printer also comprises means for holding only the data of the one line in the circuit 35 by transferring only the data of the one line when the plurality of the data are compared at the respective lines, if the data of at least two dot lines are the same and printing the line according to the held data. In this case, only the data of the one line is transferred to a print head.