The invention relates to a PLC apparatus which is capable of predicting its life expectancy depending on an ambient temperature of the PLC apparatus. The PLC apparatus includes: an input unit through which a user inputs an ambient temperature of a PLC; a memory in which a life expectancy of a part depending on the ambient temperature is stored; a diagnosing unit configured to predict the PLC life expectancy by calculating a ratio of part life expectancy corresponding to the input ambient temperature to reference life given when the PLC is made, and compare PLC used time and the PLC life expectancy to determine whether or not the PLC used time exceeds the PLC life expectancy; and a control unit configured to control the operation of the input unit, the memory and the diagnosing unit.