A lens apparatus for a surveillance camera. The apparatus includes an operation ring which is rotatably provided on an outer periphery of a lens barrel body, a threaded hole being formed in an outer peripheral surface of the operation ring. The apparatus also includes a cover which is provided on the lens barrel body to cover an outer periphery of the operation ring, a slit which is circumferentially formed in a peripheral surface of the cover. The apparatus further includes a knob which has a body part and a threaded part and is attached to the operation ring by screwing the threaded part into the threaded hole through the slit. The operation ring is locked by tightening the knob and holding the cover between the operation ring and the body part of the knob.