Ink drying apparatus for drying ink by heat after printing

A compact ink drying apparatus is capable of drying ink ejected to a resin substrate. The ink drying apparatus has a hot air dryer, a hot air supplying part, and an exhausting part. The hot air dryer has a drying furnace, a substrate conveying path formed as a spirally shaped path in the drying furnace, and substrate drying ducts blowing hot air to a surface of a resin substrate on which ink is ejected conveyed along the substrate conveying path to heat ink and exhausting water vapor generated by heating of ink. The hot air supplying part is outside the drying furnace and supplies hot air into the substrate drying ducts, and the exhausting part is outside the drying furnace and exhausts air in the drying furnace through the substrate drying ducts.