A surface detection apparatus for a blast furnace, the surface detection apparatus to be equipped outside the blast furnace, the surface detection apparatus configured to transmit a detection wave from a transceiver, from an antenna toward a reflection plate, wherein the detection wave is reflected on the reflection plate and transmitted into the furnace through an opening portion of the blast furnace, the detection wave, which has been reflected on a surface of a burden in the furnace and has reached the reflection plate through the opening portion, is reflected on the reflection plate, and the reflected detection wave is transmitted toward the antenna, the surface detection apparatus configured to receive the detection wave at the transceiver, thereby detecting a surface profile of the burden, the surface detection apparatus comprising: a container adapted to be attached to the opening portion, the container having a bottom surface a part of which is opened in correspondence to the opening portion; the reflection plate adapted to be disposed in the container immediately above the opening portion; and the antenna disposed to face the reflection plate and fixed to the container; and a tilt angle varying mechanism provided in a space of a side of the reflection plate opposite to the antenna and configured to vary a tilt angle of the reflection plate with respect to an antenna side or an anti-antenna side, and a rotation mechanism configured to rotate the reflection plate by a predetermined angle about a propagation axis of the detection wave, wherein the tilt angle varying mechanism comprises a first link one end of which is fixed to an opposite surface of the reflection plate to the antenna, a second link coupled to the first link via a coupling pin, a slider coupled to the second link via a coupling pin, and a slider driving means (210, 208) for advancing or retreating the slider to the antenna side or the anti-antenna side, the rotation mechanism comprises a support arm configured to rotatably support support shafts protruding from both diametrical ends of the reflection plate, a pipe body to which the support arm is attached, and a pipe body rotating means for rotating the pipe body about an axis of the pipe body, the tilt angle varying mechanism and the rotation mechanism have a double pipe structure where the slider is an inner pipe and the pipe body is an outer pipe, and the tilt angle varying mechanism and the rotation mechanism are configured to be driven in cooperation to linearly or planarly scan the detection wave on the surface of the burden. a container adapted to be attached to the opening portion, the container having a bottom surface a part of which is opened in correspondence to the opening portion; the reflection plate adapted to be disposed in the container immediately above the opening portion; and the antenna disposed to face the reflection plate and fixed to the container; and a tilt angle varying mechanism provided in a space of a side of the reflection plate opposite to the antenna and configured to vary a tilt angle of the reflection plate with respect to an antenna side or an anti-antenna side, and a rotation mechanism configured to rotate the reflection plate by a predetermined angle about a propagation axis of the detection wave, wherein the tilt angle varying mechanism comprises a first link one end of which is fixed to an opposite surface of the reflection plate to the antenna, a second link coupled to the first link via a coupling pin, a slider coupled to the second link via a coupling pin, and a slider driving means (210, 208) for advancing or retreating the slider to the antenna side or the anti-antenna side, the rotation mechanism comprises a support arm configured to rotatably support support shafts protruding from both diametrical ends of the reflection plate, a pipe body to which the support arm is attached, and a pipe body rotating means for rotating the pipe body about an axis of the pipe body, the tilt angle varying mechanism and the rotation mechanism have a double pipe structure where the slider is an inner pipe and the pipe body is an outer pipe, and the tilt angle varying mechanism and the rotation mechanism are configured to be driven in cooperation to linearly or planarly scan the detection wave on the surface of the burden.