A vibrating device includes a drive unit configured to drive a vibrating member to produce vibration Z(x,y) at a dust-screening member, the vibration being expressed as follows: Z(x,y)=Wmn(x,y)·cos(γ)+Wnm(x,y)·sin(γ) where Z(x,y) is vibration at a given point P(x,y) on the dust-screening member, m and n are positive integers including 0, indicating the order of natural vibration corresponding to a vibrational mode, W mn ⁡ ( x , y ) = sin ⁡ ( n ⁢ ⁢ π · x + π 2 ) · sin ⁡ ( m ⁢ ⁢ π · y + π 2 ) , ⁢ W nm ⁡ ( x , y ) = sin ⁡ ( m ⁢ ⁢ π · x + π 2 ) · sin ⁡ ( n ⁢ ⁢ π · y + π 2 ) , and γ is +π/4 or ranges from −π/8 to −π/4. LP/LF is 0.5 or more, but less than 1, where LF is the length of the sides to which the vibrating member is arranged in a virtual rectangle having the same area as the surface of the dust-screening member and sides including the one side, and LB is the longitudinal length of the vibrating member of the sides parallel to the one side.