A coding apparatus (100, 200) for coding audio signal comprising: a first coding section (104, 223) adapted to code a low frequency band spectrum of an input signal; and a second coding section (105, 210) adapted to perform coding processing on a high frequency band spectrum of the input signal; wherein the second coding section (105, 210) comprises: a third coding section (112, 203) adapted to code a shape of the high frequency band spectrum of the input signal; a fourth coding section (113, 206) adapted to code a respective gain of at least one specific subband in a plurality of subbands forming the high frequency band spectrum; and a first output section (114, 207) adapted to output coded information obtained in the third and fourth coding sections; and wherein the apparatus further comprises a second output section (106, 227) adapted to output coded information obtained in the first and second coding sections; characterized in that the fourth coding section (113, 206) comprises an interpolation section (126, 216) adapted to interpolate a respective gain of each of the plurality of subbands in the high frequency band spectrum other than the at least one specific subband by using: the gain of the specific subband and a gain of a highest-frequency subband in the low frequency band spectrum, if only the gain of one specific subband of the high frequency band spectrum is coded by the fourth coding section (113, 206), or the gains of the specific subbands, if the gains of at least two specific subbands of the high frequency band spectrum are coded by the fourth coding section (113, 206). a first coding section (104, 223) adapted to code a low frequency band spectrum of an input signal; and a second coding section (105, 210) adapted to perform coding processing on a high frequency band spectrum of the input signal; wherein the second coding section (105, 210) comprises: a third coding section (112, 203) adapted to code a shape of the high frequency band spectrum of the input signal; a fourth coding section (113, 206) adapted to code a respective gain of at least one specific subband in a plurality of subbands forming the high frequency band spectrum; and a first output section (114, 207) adapted to output coded information obtained in the third and fourth coding sections; a third coding section (112, 203) adapted to code a shape of the high frequency band spectrum of the input signal; a fourth coding section (113, 206) adapted to code a respective gain of at least one specific subband in a plurality of subbands forming the high frequency band spectrum; and a first output section (114, 207) adapted to output coded information obtained in the third and fourth coding sections; and wherein the apparatus further comprises a second output section (106, 227) adapted to output coded information obtained in the first and second coding sections; characterized in that the fourth coding section (113, 206) comprises an interpolation section (126, 216) adapted to interpolate a respective gain of each of the plurality of subbands in the high frequency band spectrum other than the at least one specific subband by using: the gain of the specific subband and a gain of a highest-frequency subband in the low frequency band spectrum, if only the gain of one specific subband of the high frequency band spectrum is coded by the fourth coding section (113, 206), or the gains of the specific subbands, if the gains of at least two specific subbands of the high frequency band spectrum are coded by the fourth coding section (113, 206). the gain of the specific subband and a gain of a highest-frequency subband in the low frequency band spectrum, if only the gain of one specific subband of the high frequency band spectrum is coded by the fourth coding section (113, 206), or the gains of the specific subbands, if the gains of at least two specific subbands of the high frequency band spectrum are coded by the fourth coding section (113, 206).