PURPOSE: To provide the driving system while enables to print with a uniform density over the entire width by regulating the voltage applied to a block having a smaller number of heating resistors, in the thermal head wherein one scanning row consists of a plurality of heating resistors.

CONSTITUTION: The heating resistors 2 are divided into a plurality of blocks 51, 52...5n-1, 5n, each of which includes a predetermined number of the resistors 2, and the resistor groups are connected to a power source 5 through source drive transistors 61W6n respectively. In the last block 5n, the number of the resistors 2 is smaller than those in the other blocks, and a balance resistance 9 is provided between corresponding diodes 3 and the emitter 6nE of the transistor 6n. Since the block 5n includes a smaller number of resistors, a smaller amount of power is consumed during printing, so that a greater amount of current is apt to flow through the resistors 2 in this block. However, by causing a voltage drop at the resistance 9, the current flowing through the resistors 2 in the block 5n is made equal to that flowing through the resistors 2 in the other blocks.