A brake device (100; 200; 300; 400) comprising: an outer race having a cylindrical inner peripheral surface; at least two brake cams (20; 220; 320) arranged inside the outer race in a circumferential direction, each brake cam (20; 220; 320) having two brake surfaces (21; 221; 321) and a cam-side contact portion (23; 223; 323), the brake surfaces (21; 221; 321) being provided at both ends in the circumferential direction of a radially outer side of the brake cam (20; 220; 320) and configured to be contactable with the inner peripheral surface of the outer race, the cam-side contact portion (23; 223; 323) being provided at a radially inner side of the brake cam (20; 220; 320), the brake cams (20; 220; 320) being configured to engage with an input-side rotary member (42; 242) and receive a rotation moment from the input-side rotary member (40; 240); and an output-side rotary member (30; 230; 330; 430) arranged at radially inner sides of the brake cams (20; 220; 320), the output-side rotary member (30; 230; 330; 430) including output-side contact portions (33A, 33B) contactable with the cam-side contact portion (23; 223; 323), wherein a rotation moment of the input-side rotary member (42; 242) received by the brake cams (20; 220; 320) is transmitted to the output-side rotary member (30; 230; 330; 430) to cause the output-side rotary member (30; 230; 330; 430) to rotate, while a rotation moment of the output-side rotary member (30; 230; 330; 430), as effected in at least one direction, received from the output-side rotary member (30; 230; 330; 430) by the brake cams (20; 220; 320) fails to cause the brake cams (20; 220; 320) to move, and characterized in that each of the cam-side contact portions (23; 223; 323) of the respective brake cams (20; 220; 320) is formed as a flat surface facing the radially inner side, wherein the output-side contact portions (33A, 33B) are contactable with the flat surfaces of the cam-side contact portions (23; 223; 323) of the respective brake cams (20; 220; 320) in positions each shifted from a center plane that is a plane containing a center axis of the inner peripheral surface of the outer race and a midpoint between inner ends of the two brake surfaces (21; 221; 321) located at the both ends of a corresponding brake cam (20; 220; 320), wherein regions of the cam-side contact portions (23; 223; 323) of the respective brake cams (20; 220; 320), which are contactable with the output-side contact portions (33A, 33B), are on a both-end reference plane connecting outer ends of the two brake surfaces (21; 221; 321) of a corresponding brake cam (20; 220; 320), or on an axis-of-rotation side that is one side of the both-end reference plane on which an axis of rotation of the output-side rotary member (30; 230; 330; 430) is located. an outer race having a cylindrical inner peripheral surface; at least two brake cams (20; 220; 320) arranged inside the outer race in a circumferential direction, each brake cam (20; 220; 320) having two brake surfaces (21; 221; 321) and a cam-side contact portion (23; 223; 323), the brake surfaces (21; 221; 321) being provided at both ends in the circumferential direction of a radially outer side of the brake cam (20; 220; 320) and configured to be contactable with the inner peripheral surface of the outer race, the cam-side contact portion (23; 223; 323) being provided at a radially inner side of the brake cam (20; 220; 320), the brake cams (20; 220; 320) being configured to engage with an input-side rotary member (42; 242) and receive a rotation moment from the input-side rotary member (40; 240); and an output-side rotary member (30; 230; 330; 430) arranged at radially inner sides of the brake cams (20; 220; 320), the output-side rotary member (30; 230; 330; 430) including output-side contact portions (33A, 33B) contactable with the cam-side contact portion (23; 223; 323), wherein a rotation moment of the input-side rotary member (42; 242) received by the brake cams (20; 220; 320) is transmitted to the output-side rotary member (30; 230; 330; 430) to cause the output-side rotary member (30; 230; 330; 430) to rotate, while a rotation moment of the output-side rotary member (30; 230; 330; 430), as effected in at least one direction, received from the output-side rotary member (30; 230; 330; 430) by the brake cams (20; 220; 320) fails to cause the brake cams (20; 220; 320) to move, and characterized in that each of the cam-side contact portions (23; 223; 323) of the respective brake cams (20; 220; 320) is formed as a flat surface facing the radially inner side, wherein the output-side contact portions (33A, 33B) are contactable with the flat surfaces of the cam-side contact portions (23; 223; 323) of the respective brake cams (20; 220; 320) in positions each shifted from a center plane that is a plane containing a center axis of the inner peripheral surface of the outer race and a midpoint between inner ends of the two brake surfaces (21; 221; 321) located at the both ends of a corresponding brake cam (20; 220; 320), wherein regions of the cam-side contact portions (23; 223; 323) of the respective brake cams (20; 220; 320), which are contactable with the output-side contact portions (33A, 33B), are on a both-end reference plane connecting outer ends of the two brake surfaces (21; 221; 321) of a corresponding brake cam (20; 220; 320), or on an axis-of-rotation side that is one side of the both-end reference plane on which an axis of rotation of the output-side rotary member (30; 230; 330; 430) is located.