A light attaching device includes a base member having a bottom portion for attaching onto a bicycle portion, a housing pivotally attached to the base member and having a lock member for engaging with a spring latch of the base member and having an internal gear. A coupling strap may detachably attach the base member to the bicycle portion. A shaft is slidably engaged in the housing and has a gear for meshing with the internal gear of the housing and for adjustably positioning the shaft to the housing at selected angular position. A light device may be attached to the shaft and adjusted relative to the housing at the selected angular position together with the shaft.