Edit in JSFiddle

var chart = c3.generate({
  bindto: "#combochart",
  data: {
    x: "year",
    columns: [
      ["year", "55세", "56세", "57세", "58세", "59세", "60세", "61세", "62세", "63세", "64세", "65세", "66세", "67세", "68세", "69세", "70세", "71세"],
      ["pension1", 1000, 900, 850, 800, 760, 720, 680, 640, 600, 600, 600, 600, 600, 600, 600, 600, 600],
      ["pension2", 800, 700, 600, 500, 400, 300, 200, 100, 0, 0, 0, 0, 0, 0, 0, 0, 0],
      ["pension3", 400, 500, 600, 650, 600, 550, 500, 400, 300, 300, 300, 300, 300, 300, 300, 300, 300],
      ["pension4", 200, 100, 300, 350, 400, 420, 450, 400, 370, 370, 370, 370, 370, 370, 370, 370, 370],
      ["total", 2400, 2200, 2350, 2300, 2160, 2010, 1830, 1540, 1270, 1270, 1270, 1270, 1270, 1270, 1270, 1270, 1270],
    ],
    types: {
      pension1: "area",
      pension2: "area-spline",
      pension3: "area",
      pension4: "area-spline",
      total: "bar",
    },
    colors: {
      total: "#1ab394",
      pension1: "#337ab7",
      pension2: "#328cc1",
      pension3: "#329ecb",
      pension4: "#31b0d5",
    },
  },
  bar: {
    width: {
      ratio: 0.2,            
    },
  },
  axis: {
    x: {
      type: "category",
    },
  },
});

<div id="combochart"></div>