PROBLEM TO BE SOLVED: To effectively reduce an influence of an ultra-low frequency sound on an object with simple configurations.SOLUTION: A microphone 14 detects information related to a first ultra-low frequency sound S1. A signal processing part 16 generates a signal of a phase reverse to that of a first ultra-low frequency sound S1 on the basis of the information detected by the microphone 14. The controller 18 allows sound generation means 20 to generate a second ultra-low frequency sound S2 of a phase reverse to that of the first ultra-low frequency sound S1 which is large enough to offset the first ultra-low frequency sound S1 by driving the sound generation means 20 on the basis of the signal supplied from the signal processing part 16. The sound generation means 20 is arranged such that the first ultra-low frequency sound S1 during the transmission of the second ultra-low frequency sound S2 from a diesel engine 2A to an object 4 is oriented. The first ultra-low frequency sound S1 and the second ultra
