A flat speaker includes a diaphragm having a flat plate shape, a drive unit that is attached to a back surface of the diaphragm and vibrates the diaphragm, a fixing member that fixes an outer circumference of the diaphragm in a circumferential direction, a first support member that is disposed on an inner side in a radial direction of the fixing member, supports the back surface of the diaphragm in the circumferential direction, and has a value of hardness smaller than a value of hardness of the fixing member and/or a value of internal loss larger than a value of internal loss of the fixing member, and a second support member that is disposed on an inner side in the radial direction of the first support member, supports the back surface of the diaphragm in the circumferential direction, and has a value of hardness smaller than the value of hardness of the first support member and/or a value of internal loss larger than the value of internal loss of the first support member.