A picture coding device for coding a moving picture using inter prediction based on inter prediction information in units of blocks, the picture coding device comprising: a coding information storage unit configured to store inter prediction information used in the inter prediction of a coded block in a history-based motion vector predictor candidate list; a spatial merging candidate derivation unit configured to derive a spatial merging candidate from inter prediction information of a block spatially neighboring a coding target block and to add the spatial merging candidate to a merging candidate list; a temporal merging candidate derivation unit configured to derive a temporal merging candidate from inter prediction information of a block located at the same position as or near the coding target block in a picture of a different time, and to add the temporal merging candidate to the merging candidate list; and a history-based merging candidate derivation unit configured to derive a history-based merging candidate from the inter prediction information stored in the history-based motion vector predictor candidate list and to add the history-based merging candidate to the merging candidate list, wherein the history-based merging candidate derivation unit compares a predetermined number of inter prediction information elements from the most recently added element of the history-based motion vector predictor candidate list with the spatial merging candidate and adds an inter prediction information element of the history-based motion vector predictor candidate list to the merging candidate list as the history-based merging candidate when a value of the inter prediction information element of the history-based motion vector predictor candidate list is different from a value of inter prediction information of the spatial merging candidate, said predetermined number being smaller than number of elements stored in the history-based motion vector predictor candidate list, characterized in that the history-based merging candidate derivation unit thereafter adds the inter prediction information elements stored prior to the predetermined number of the inter prediction information elements to the merging candidate list as the history-based merging candidates without making a comparison with the merging candidates in the list. a coding information storage unit configured to store inter prediction information used in the inter prediction of a coded block in a history-based motion vector predictor candidate list; a spatial merging candidate derivation unit configured to derive a spatial merging candidate from inter prediction information of a block spatially neighboring a coding target block and to add the spatial merging candidate to a merging candidate list; a temporal merging candidate derivation unit configured to derive a temporal merging candidate from inter prediction information of a block located at the same position as or near the coding target block in a picture of a different time, and to add the temporal merging candidate to the merging candidate list; and a history-based merging candidate derivation unit configured to derive a history-based merging candidate from the inter prediction information stored in the history-based motion vector predictor candidate list and to add the history-based merging candidate to the merging candidate list, wherein the history-based merging candidate derivation unit compares a predetermined number of inter prediction information elements from the most recently added element of the history-based motion vector predictor candidate list with the spatial merging candidate and adds an inter prediction information element of the history-based motion vector predictor candidate list to the merging candidate list as the history-based merging candidate when a value of the inter prediction information element of the history-based motion vector predictor candidate list is different from a value of inter prediction information of the spatial merging candidate, said predetermined number being smaller than number of elements stored in the history-based motion vector predictor candidate list, characterized in that the history-based merging candidate derivation unit thereafter adds the inter prediction information elements stored prior to the predetermined number of the inter prediction information elements to the merging candidate list as the history-based merging candidates without making a comparison with the merging candidates in the list.