To improve drying efficiency by improving draining of a filter, by drying the filter by the proper air volume in response to performance of the filter to be dried.

Hot air is generated by heating air sucked in via the filter 12 by operation of a blower 14 by a heater 16. This hot air is supplied to a filter holder 34 for holding a drying object filter 1 via a hot air conduit 20, so as to cross a filter surface of the drying object filter 1. An air volume adjuster 22 switches the air volume of the blower 14 in response to a particle collecting rate of the drying object filter 1. The filter holder 34 holds the drying object filter 1 so that the filter surface of the drying object filter 1 becomes vertical and a peripheral surface becomes oblique.