A surface detection apparatus for a blast furnace is provided. An antenna is fixed to a side of a container attached to an opening portion of the blast furnace and having a bottom surface opened in correspondence to the opening portion. A reflection plate is disposed in the container immediately above the opening portion so as to face the opening portion and the antenna. A tilt angle varying mechanism and a rotation mechanism for the reflection plate are configured as a double pipe structure and are provided at an anti-antenna side of the reflection plate.