Abstract: An arm driving device for a fluid loading apparatus is disclosed, which comprises a V link comprised of a first link arm and a second link arm connected together rotatably at one end thereof and a hydraulic cylinder having a cylinder rod the top of which is rotatably connected to a suitable portion of either of the link arms, the other end of the first link arm being connected rotatably to a suitable portion of an extension member of an inboard arm of the fluid loading apparatus and the other end of the second link arm being connected rotatable to a suitable member fixedly connected to a stand pipe installed on land. The arm driving device may be applied to operate the outboard arm of the fluid loading apparatus with respect to the inboard arm.