A warning sound generating device includes a sound source member and an enclosure for protecting the sound source member. A front wall of the enclosure and a sound emitting portion of the sound source member face each other. The front wall of the enclosure has at least one continuous projecting wall extending toward the sound source member. The sound source member has at least one continuous projecting wall extending toward the enclosure and surrounding the sound emitting portion. The enclosure has a plurality of sound exits formed outwardly from the outermost projectng wall of the enclosure. The projecting walls of the sound source member and the enclosure cooperate to define a sound passageway through which a sound generated from the sound emitting portion passes. Each of the projecting walls has a thickness decreasing from the base to the forward rim thereof, so that the passageway has a width between the projecting walls increasing from the sound emitting portion to the sound exits.