A fiber cleaver is provided which is capable of cleaving a glass fiber portion in a short time without depending on a particular working environment. The fiber cleaver comprises a holding member for holding a glass fiber portion of an optical fiber, a cutter for affording a scratch to the glass fiber portion which is held by the holding member, an elastic member or spring for moving the cutter, and a slider engaging member for maintaining the elastic member or spring in a state of elastic deformation. Also provided is a fiber cleaver comprising a holding member for holding the glass fiber portion of an optical fiber, a cutter for affording a scratch to the glass fiber portion held by the holding member, and a holder engaging part for holding a holder that holds an optical fiber at its part having a protective covering. The holder engaging part has a first holder engaging member for pushing and holding the holder in a direction parallel to a movement direction of the cutter.