and can only go straight when releasing the set direction it is necessary to press down the pressure part 50 of the release mechanism at this time the engaging convex body 402 of the front of the pressure platelet on directional system 4 will separate from the engaging part 53 of release mechanism 5 positioning platelet 41 will be affected by elastic platelet 4101 and 4111 and spring out of the positioning trough at the same time pressure platelet 40 will spring back to its original horizontal position thus the direction setting of wheel 27 is released as shown in fig7 8 another real embodiment of this invention is comprised castor main body 2 brake system 3 release mechanism 5 and several positioning elements 6 the castor main boy 2 there is the direction change center 39 s revolving connecting base 20 under which there is direction change engaging fluted disc 200 and inside castor main body 2 on the concave surface there is a positioning convex body 21 and positioning holes 22 23 and 24 and the front of the castor main body there is a convex surface 25 and under the castor main body convex surface there is a pin joint hole 26 wheel 27 and cover 270 the brake system 3 is inside the concave surface of the bottom of castor main body 2 and includes pressure platelet 30 and brake direction change body 31 and other parts on the front of the pressure platelet 30 is the pressure part.