The present invention provides a heat package wherein a surface of a generating heat element that generates heat when exposed to atmosphere is placed against or attached to a heat conductive member. The shoe cover is preferably formed of a flexible plastic material and is generally \u201cU\u201d shaped to fit around the top and side portions of a shoe. A head driving power circuit incorporated in the printing apparatus compares a value obtained by dividing the reference voltage with a value obtained by dividing the output voltage from the power circuit and performs control so as to eliminate an error. The IO interface receives a program code provided externally.