To accurately measure a front reflection factor by the nondestructive method by calculating the front reflection factor of an optical function film for preventing light- transmitting type reflection from a rear reflection factor, a total reflection factor, and a transmission rate.

A reference rear reflection factor is calculated in advance for a representative light-transmission-type optical function film for preventing reflection. Actual total reflection rate and transmission rate are measured in real time for the light-reflection type optical function film for preventing reflection to be measured. By substituting a reference rear reflection factor that is obtained in advance, a total reflection factor being measured for the light- transmitting type optical function film for preventing reflection to be measured, and transmittance for an operation expression, the front reflection factor of the light-transmitting type optical function film for preventing reflection is calculated, thus accurately calculating the surface reflection factor of the optical function film, without coating the rear of the light- transmission-type optical function film for preventing reflection with a black paint, namely without destroying the light-transmitting type optical function film for preventing reflection.