PURPOSE: To make the device small in size and light in weight and to obtain stable running when a space between walls is narrow and direction change without radius, by providing wheels on the back of both ends of a pair of frames intersecting crosswise.

CONSTITUTION: Contact pressure of driving wheels 23, 24 and driven wheels 32, 33 to double walls is obtained by pushing out one frame 22 out of a pair of frames intersecting crosswise by a thrusting mechanism 30 at fixed pressure against another frame. Accordingly, own weight is held by frictional force of wheels and wall faces, and the device can run in all directions including vertical upward movement, inclined movement etc. Running power is obtained by forced rotation driving of wheels 23, 24. Direction of rotation of wheels 23, 24, 32, 33 can be changed freely, and the testing machine can change direction of advance freely, and can make running of direction change locus having no radius of curvature.