There is prepared a printing plate on which a material being hydrophilic at a first temperature and being hydrophobic at a second temperature which is lower than the first temperature is provided. First, the whole surface of the printing plate is forcibly made either one of hydrophobic or hydrophilic. Next, a region having the other nature out of hydrophobic and hydrophilic is formed so as to correspond to an image to be printed. Then, ink is supplied onto the region having hydrophobic nature to conduct offset printing.