There is a great need for the development of a robot to perform painting and cleaning of high-rise buildings and tanks to perform painting and cleaning of high-rise buildings and tanks and similar dangerous tasks. The Mechanical Engineering Laboratory has been developing a wall-climbing robot (MEL-SPIDER) which can adhere to rough finished wall using vacuum suction cups and can move up and down as well as to the right and left. Two prototypes were studied : a separate type (MSII) and a self contained type(MSIII). For the separate type, the power / control unit was set on the ground separated from the main mobile unit. Power and control signals were supplied to the main mobile unit by pneumatic tubes and electric cables. The MS I I has eight legs and each leg terminates with a vacuum suction cup. Each cup comprises a metallic disk with a closed - cell foamed rubber sealing ring around the edge. The vacuum for the suction cup is supplied by a vacuum pump in the power / control unit. The eight legs are in two groups of four legs each. Climbing is achieved by moving the two groups alternately while synchronizing the suction and release control signals for their suction cups. Movement is achieved by DC servo motors. The MS I I weigh 17 kg and it's dimensions are 85 cm(L) 55 cm(w) 25 cm(H) . Climbing experiments on vertical walls of concrete buildings were successful, and many points to be improved concerning adhering and climbing methods were found. These improvements were incorporated in the development of MS I I I which carries all devices including the power source and controller. The MS I I I uses an engine to drive both a generator and vacuum pump and it's movement is remotely controlled by the operator. The MS I I I weighs 35 kg and it's dimensions are 100 cm(L) 58 cm(W) 32 cm(H). Climbing tests on the wall were successful, and the technical possibility of this moving method on vertical walls was presented.