The use of antimicrobial agents in food-producing animals may lead to the emergence and spread of antimicrobial resistance in bacteria of animal origin. The use of antimicrobial agents in pigs in 2018 in Japan was evaluated in terms of the weight of active ingredient and number of defined daily doses (DDD), using annual sales data of veterinary antimicrobials sold for use in pigs. In addition, the use of antimicrobial agents in the Japanese pig sector in 2008 to 2017 was evaluated to determine whether or not there were any differences in temporal change pattern by use of different metrics. In 2018, 447 metric tons of active ingredient, corresponding to 77,379 × 106 kg-days (Japanese DDD) and 34,903 × 106 kg-days (European DDD) were sold. The proportion of the sales amount of sulfonamides, trimethoprim and lincosamides to the total sales amount was significantly different depending on the metric used. For most antimicrobial classes, the number of Japanese DDDs was greater than the number of European DDDs. These results indicate that the DDD-based metric, which is more reflective of the selective pressure of antimicrobials, is recommended for use in monitoring the antimicrobial use in pigs in Japan. The differences in the number of Japanese DDDs and European DDDs appear to confirm the need for Japanese DDDs.