A keyboard scan circuit for a device receiving plural inputs simultaneously is provided. The scan circuit includes a plurality of keyboard input/output ports, each of which can be selected from a group consisting of an input mode, an output mode, and a floating mode for receiving one of a plural inputs, a plurality of rectangular matrices including a plurality of detectable input terminals and a plurality of synchronously detectable input terminals and formed by means of cross-linking the keyboard input/output ports, and a plurality of current-isolating elements electrically connected between the keyboard input/output ports and the rectangular matrices for mutually isolating signals of the rectangular matrices.