The present invention provides an interdental brush and a cap, said brush having a good handling property and a low manufacturing cost, said brush being stored with the cap on while adjusting the brush body at any angle. The handle member 3 supporting the brush body 2 includes a handle body 6, an arm 12 extending from one end of the handle body 6, a brush support 13 that holds a base of the brush body 2, a first hinge 14 that connects the tip of the arm 12 and one end of the brush support 13 in a freely rotating manner, an operating portion 15 provided slidably at the other end of the handle member 3, and a second hinge 16 that connects the tip of the operating portion 15 and the other end of the brush support 13 in a freely rotating manner.