Abstract: A thermal head is arranged in a printing device so as to be opposite to a printed object fed in a constant direction. The thermal head comprises a base member; a plurality of heating resistors arranged in the base member; electrodes disposed in the base member corresponding to the heating resistors; and a slit formed on a surface of the heating resistors and having a shape in which the width of the slit in a feeding direction of the printed object is less than that in an arranging direction of the heating resistors perpendicular to the feeding direction and the width of the slit in the arranging direction of the heating resistors is approximately equal to a half length of a pitch of the heating resistors in the arranging direction thereof. The accuracy in circularity of dots is improved by satisfying a condition that the width of the slit in the feeding direction of the printed object is less than that in the arranging direction of the heating resistors perpendicular to the feeding direction.