A braking and steering mechanism for use in a mobile G-arm of an X-ray imaging apparatus. A frame (1) thereof has a lower portion rotatably fitted, via a support (3), with a guide wheel (4) on both ends, the support (3) is rotatably fitted on the frame (1), and the guide wheels (4) are rotatably fitted on the support (3). A brake lever (5) is slidably disposed above the guide wheel (4) and on the frame (1), and is sleeved with a reset compression spring (6). The frame (1) is rotatably fitted with a transmission shaft (7), both ends of the transmission shaft (7) are provided with brake cams (8) respectively pressing against upper ends of corresponding brake levers (5), and the transmission shaft (7) is unrotatably provided with a pedal. Inclination of the pedal drives the brake cams (8) to rotate, such that the brake cams (8) overcome the force of the reset compression springs (6) and press the brake levers (5) against the guide wheels (4). The brake cams (8) at the two ends of the transmission shaft (7) of the braking and steering mechanism push and press the corresponding brake levers (5) downward along with the inclination of the pedal, such that the two brake levers (5) simultaneously press tightly against the two guide wheels (4). When the pedal is released, the brake levers (5) move upward under the action of the reset compression springs (6) and release the guide wheels (4) to stop braking. In this way, the present invention greatly saves time for an operator.La présente invention concerne un mécanisme de freinage et dorientation pour utilisation dans un bras en G mobile dun appareil dimagerie à rayons X. Un cadre (1) de celui-ci comporte une partie inférieure ajustée de façon rotative, par lintermédiaire dun support (3), avec une roue de guidage (4) sur les deux extrémités, le support (3) est ajusté de façon rotative sur le cadre (1), et les roues de guidage (4) sont ajustées de façon rotative sur le support (3). Un levier de frein (5) est disposé de façon co
