A keyboard-video-mouse (KVM) switch has been developed as an important solution for allowing a user to manage a plurality of computers via a console station, including a video monitor, keyboard, and mouse.  Further, KVM cables are utilized to connect the KVM switch to each computer.  The KVM switch enables the keyboard, video monitor and mouse to control more than one computer at a time.  Basically, the user utilizes the video monitor, keyboard, and mouse to operate a currently selected computer, and utilizes a hot key on the keyboard or a port-selecting button on the KVM switch to switch the currently selected computer to a next selectable computer.  The KVM switch transmits the switch signals among the computers and the video monitor, keyboard, and mouse depending on which computer is currently selected. 
However, it is still inconvenient that the user must remember the hot key or move to press the port-selecting button in order to control the KVM switch.  Further, TW patent application NO.  92219775, issued on Oct. 11, 2004, discloses a computer host switch that a control circuit controls a mouse to switch a plurality of computer hosts.  However, because three or more keys of the mouse are needed and it is too complicated so that the control circuit cannot easily switch the computer hosts.  In addition, the publication document in website: http://www.cctch.com.tw/products/showproduct.jsp?ID=97 discloses a KVM switch of Product ID: IC-A12-M. The KVM switch cannot effectively switch the computers via a mouse because of a complicated mouse clicking manner. 
For the convenience of use, there is a need to provide a novel KVM switch for switching a plurality of computers using a mouse.