To reduce noise during blade rotation in a testing device of a blade.

Blades 53 for a helicopter are supported on a stand 54, rotated by a driving device in the testing device 11, and tested in relation to various items. In the testing device 10, a ceiling panel 11 is supported by columns 13, an upper sound proofing wall 12b is mounted to the peripheral part under the panel 11, the wall 12b has a tapered shape with a small diameter and contacts with a cylindrical lower sound proofing wall 12a, and the circumference of the lower end of the sound proofing wall opens. When the blades 53 rotate, air is sucked by many clearances 24 formed with a sound absorbing material 21 of the ceiling panel 11, enters to the inside after the sound absorbing, is collected to the inside in a tapered part of the sound proofing wall 12b, is pressed down by the blades 53, and flows out of the opening around the lower end of the sound proofing wall.