Both ends of an interface may each be configured by an interface device including a light emitting unit that emits light into a textile, a light diffusion unit that widely diffuses the emitted light onto the textile and extends a light receiving range of a light receiving unit, and a light receiving unit for receiving an optical signal of the other party unlike the existing method using electromagnetic inductive coupling in the wearable computing system and a method of performing communication by using light such as infrared rays, visible light, laser, or the like as a medium is provided.