An image can be read during main scanning under an optimized image reading condition even if dust is attached to a document such as a photographic film or the like, or if there are scratches. The actuator includes first and second anchors secured to the substrate and a floating shuttle positioned movably parallel to the substrate. The power control module may set an input signal to a first level and may gradually vary the level of the input signal to be substantially equal to its original level and to adjust a gain of the transmitter to transmit at the targeted power level. A controlling disk is rotatably connected to a side face of the hollow cylindrical body to control pivotal movement of the bit compartments so that rotation of the controlling disk is able to pivot the bit compartments relative to the hollow cylindrical body to reveal the bits received in the holes of the bit compartments. Thus the user does not have to stretch his forward arm as far relative to the rear handle as he would have to do when using the handle assembly of a conventional power tool of this type.