To automate complete drying of a solvent which is a dried object and to obtain an excellent surface state of a dried body after dried.

A control part 7 obtains a drying time t based on an expression (1) according to the material property of the solvent which is the dried object, and holds the degree of vacuum in a vacuum chamber 1 to the steam pressure of the solvent at least for the time t. The expression (1) is t=(6RH)/kTPe [wherein: is a viscosity (Pa S) of the solvent; R is an atomic radius=particle diameter (m) of particles such as powder included in the solvent; H is an applied film thickness of the solvent; k is a Boltzmann coefficient (J/K); T is a temperature T(K) of the solvent; Pe is a Peclet number=EH/D; E is a solvent film contraction speed (m/s); and D is a Brown diffusion factor (m2/s)=kT/(6R)].