To provide a drying device that can optimize the amount of heat to be applied to a material to be dried.

The inside of a drying hopper 2 is divided into a zone Z1 surrounded by a heater 6, a zone Z2 surrounded by a heater 7, and a zone Z3 surrounded by a heater 8, in a direction from an upper surface to a lower end. A resin material is supplied into the drying hopper 2 from the upper surface of the drying hopper 2, and is discharged from the lower end of the drying hopper 2 after passing the respective zones Z1, Z2, Z3, sequentially. In the zones Z1, Z2, Z3, the amount of heat retained in the resin material is increased by an additional amount of heat from a reference point in predetermined increase time. After the resin material is kept retaining the reference point and the additional amount of heat for predetermined heat retention time, a cycle of heat amount change for reducing the amount of heat retained in the resin material is independently repeated.