<div class="bl_ttl_box">
 <h2 class="bl_ttl_en">WORKS</h2>
 <span class="bl_ttl_jp">制作実績</span>
</div><!-- /.bl_ttl_box -->

.bl_ttl_box {
  position: relative;
  margin-bottom: 4em;
  padding-bottom: 3.5em;
  text-align: center;
}

@media screen and (max-width: 767px) {
 　.bl_ttl_box {
    margin-bottom: 3em;
    padding-bottom: 1.6em;
  }
}

.bl_ttl_box::after {
  content: "";
  position: absolute;
  bottom: 0;
  left: 50%;
  -webkit-transform: translateX(-50%);
  transform: translateX(-50%);
  width: 1px;
  height: 35px;
  background-color: #000;
}

@media screen and (max-width: 767px) {
  .bl_ttl_box::after {
    height: 4vw;
  }
}

.bl_ttl_en {
  margin-bottom: 0.1em;
  font-size: 3.75rem;
  font-weight: 600;
  font-family: "Noto Serif JP", serif;
  letter-spacing: 0.1em;
}

@media screen and (max-width: 767px) {
  .bl_ttl_en {
    margin-bottom: 0.3em;
    font-size: 2.5rem;
  }
}

.bl_ttl_jp {
  display: block;
}

<h2 class="el_ttl">制作実績</h2>

.el_ttl {
  margin-bottom: 1em;
  padding-bottom: 0.5em;
  font-size: 3rem;
  font-weight: 600;
  text-align: center;
  position: relative;
}

@media screen and (max-width: 767px) {
  .el_ttl {
    font-size: 2rem;
  }
}

.el_ttl::after {
  content: "";
  position: absolute;
  bottom: 0;
  left: 50%;
  -webkit-transform: translateX(-50%);
          transform: translateX(-50%);
  width: 100px;
  height: 2px;
  background: #000;
}

@media screen and (max-width: 767px) {
  .el_ttl::after {
    width: 15vw;
  }
}