In a vibration information detection step, a probe is inserted into a food sample, and any one of the displacement, the velocity or the acceleration of a vibration occurring on the probe by the insertion is detected as vibration information (step S1). In a frequency band dividing step, the vibration information is divided by a band pass filter into individual pieces of vibration information in each of a plurality of frequency bands (step S2). In a food texture index calculation step, a food texture index value based on vibrational energy per unit time in each of the frequency bands is calculated using a computer from the vibration information in each of the frequency bands and the center frequency of the corresponding frequency band (step S3).