The present invention relates to an apparatus and method for measuring thermal diffusivity using the flash method. The apparatus includes: a laser generator 60 for generating a flash beam 30; a measurement sample 10 having graphite layers 20 formed on front and rear surfaces thereof, through which the flash beam 30 passes; an infrared sensor 70 disposed at the rear of the measurement sample 10 for measuring a temperature and time at the rear surface of the measurement sample 10 from heat 40 dissipated from the measurement sample 10; and operation means 80 for performing an operation based on an output signal of the infrared sensor 70.