A flat speaker comprising a vibrating plate including a spiral voice coil, a lead portion extracted from the vice coil and reinforced by the reinforcing member, and an electric supply line; an edge portion supporting the vibrating plate; and a yoke, supporting the edge portion, on which the permanent magnet arranged to face the voice coil. The flat speaker 1 of the invention includes a vibrating membrane 2 of an insulating base film 3 with a spiral or meandering voice coil 4 formed on one or both faces thereof, a permanent magnet 5 arranged on corresponding location facing the voice coil 4; and a yoke 6 on which the permanent magnet 5 is arranged. The vibrating membrane 2 is avoided from hitting the permanent magnet by providing a perforated sheet on the back face of the yoke to control acoustic resistance.