Provided are an apparatus and method for writing data to a phase-change random access memory (PRAM) by using writing power calculation and data inversion functions, and more particularly, an apparatus and method for writing data which can minimize power consumption by calculating the power consumed while input original data or inverted data is written to a PRAM and storing the data consuming less power. A PRAM consumes a significant amount of power in order to store data in a memory cell since a large electric current is required to flow for a long period of time. According to the present invention, since the PRAM consumes different amounts of power when writing data with a value of 0 and data with a value of 1, the power consumed when input original data is stored and the power consumed when the input original data is inverted and stored are compared to each other, the data with a smaller power consumption is stored when the data is written to the PRAM as a word unit, and thus the power consumption of the PRAM can be reduced.