Disclosed is an input module of a programmable logic controller (PLC) capable of counting coefficient values of multiple channels. An input module of a PLC includes a plurality of detection units, a decision unit and a control unit. The plurality of detection units receives a pulse signal corresponding to each channel, applied from a load having a plurality of channels, detects rising and falling edges of the pulse signal, and transmits an output signal that is the detected result. The decision unit receives a plurality of output signals respectively transmitted from the plurality of detection units, detects edges of the plurality of channels, and transmits a detection signal that is the detected result. The control unit identifies the presence of occurrence of an interrupt using the detection signal transmitted from the decision unit and performs a counting process using the applied pulse signal when the interrupt occurs.