A light-beam scanning device includes a base plate having a torsion beam portion formed therein, and a mirror portion supported by the torsion beam portion and adapted to be oscillated. The light-beam scanning device includes one of a piezoelectric member, a magnetostrictive member and a permanent magnet member, which is fixed to or formed as a portion of the base plate. The mirror portion supported by the torsion beam portion is oscillated by a plate wave that is induced in the base plate by applying a voltage or electric field to the piezoelectric, magnetostrictive or permanent magnet member. The light-beam scanning device can efficiently generate a torsional oscillation in the mirror portion in a simplified structure.