An image decoding method, comprising: decoding information indicative of a fixed candidate number to be used for decoding a plurality of blocks coded using merging-mode as an inter-prediction mode, the fixed candidate number being a fixed maximum number of usable-for-merging candidates; and for a current block among the plurality of blocks: deriving a plurality of first merging candidates, wherein each merging candidate is derived based on a combination of a prediction direction, a motion vector, and a reference picture index that has been used to decode a first block, and wherein the derivation of the plurality of first merging candidates excludes, from the plurality of first merging candidates, any merging candidate that is an identical candidate, that has been coded by intra prediction, that is outside a boundary of the slice or a picture including the current block, and that is yet to be coded; determining whether or not a total number of first merging candidates is less than the fixed candidate number; when the total number of first merging candidates is less than the fixed candidate number, deriving at least one second merging candidate that is different from each of the first merging candidates until the total number of first merging candidates and second merging candidates is equal to the fixed candidate number, wherein each of the one or more second merging candidates has a different combination of a prediction direction, a motion vector, and a reference picture index from each of the first merging candidates; decoding a coded index using the fixed candidate number regardless of the total number of first merging candidates, wherein the coded index corresponds to one of the plurality of first merging candidates or one of the at least one second merging candidate; and decoding the current block using the corresponding one of the plurality of first merging candidates or one of the at least one second merging candidate. decoding information indicative of a fixed candidate number to be used for decoding a plurality of blocks coded using merging-mode as an inter-prediction mode, the fixed candidate number being a fixed maximum number of usable-for-merging candidates; and for a current block among the plurality of blocks: deriving a plurality of first merging candidates, wherein each merging candidate is derived based on a combination of a prediction direction, a motion vector, and a reference picture index that has been used to decode a first block, and wherein the derivation of the plurality of first merging candidates excludes, from the plurality of first merging candidates, any merging candidate that is an identical candidate, that has been coded by intra prediction, that is outside a boundary of the slice or a picture including the current block, and that is yet to be coded; determining whether or not a total number of first merging candidates is less than the fixed candidate number; when the total number of first merging candidates is less than the fixed candidate number, deriving at least one second merging candidate that is different from each of the first merging candidates until the total number of first merging candidates and second merging candidates is equal to the fixed candidate number, wherein each of the one or more second merging candidates has a different combination of a prediction direction, a motion vector, and a reference picture index from each of the first merging candidates; decoding a coded index using the fixed candidate number regardless of the total number of first merging candidates, wherein the coded index corresponds to one of the plurality of first merging candidates or one of the at least one second merging candidate; and decoding the current block using the corresponding one of the plurality of first merging candidates or one of the at least one second merging candidate. deriving a plurality of first merging candidates, wherein each merging candidate is derived based on a combination of a prediction direction, a motion vector, and a reference picture index that has been used to decode a first block, and wherein the derivation of the plurality of first merging candidates excludes, from the plurality of first merging candidates, any merging candidate that is an identical candidate, that has been coded by intra prediction, that is outside a boundary of the slice or a picture including the current block, and that is yet to be coded; determining whether or not a total number of first merging candidates is less than the fixed candidate number; when the total number of first merging candidates is less than the fixed candidate number, deriving at least one second merging candidate that is different from each of the first merging candidates until the total number of first merging candidates and second merging candidates is equal to the fixed candidate number, wherein each of the one or more second merging candidates has a different combination of a prediction direction, a motion vector, and a reference picture index from each of the first merging candidates; decoding a coded index using the fixed candidate number regardless of the total number of first merging candidates, wherein the coded index corresponds to one of the plurality of first merging candidates or one of the at least one second merging candidate; and decoding the current block using the corresponding one of the plurality of first merging candidates or one of the at least one second merging candidate.