1. An image coding method for coding a current block, comprising: deriving a first candidate having a first motion vector that has been used to code a first block; deriving a second candidate having a second motion vector that has been used to code a second block, the second block being different from the first block; determining whether or not a total number of candidates having the first candidate and the second candidate is less than a maximum candidate number; deriving a third candidate having a third motion vector and a fourth motion vector when the total number of candidates having the first candidate and the second candidate is less than the maximum candidate number, the third motion vector being identical to the first motion vector, the fourth motion vector being identical to the second motion vector; coding an index corresponding to a candidate having a motion vector; and generating a bitstream having the coded index, wherein the maximum candidate number is used to code the index, wherein the motion vector is used to code the current block, and wherein the candidate is one of a plurality of candidates having the first candidate, the second candidate, and the third candidate.
4. The image coding method according to claim 1 , wherein the deriving of the first candidate includes deriving a plurality of first candidates, and the image coding method further comprises: removing an unusable-for-merging candidate from the plurality of first candidates before the determining.