In a prior art slim-type high speed rotation optical disk apparatus, the side wall of the bottom chassis is bent at a bending point toward the side of the optical disk according to the configuration of the corner air window section of the chassis. According to the present invention, this bent side wall is formed so as to have a first vertical wall which is adjacent to the bending point and a second vertical wall which is adjacent to and lower than the first vertical wall. This constitutes an L-shaped vertical wall in the air window section of the bottom chassis, resulting in reduced noise.