Abstract: A method and apparatus for inspecting cigarette paper of eventual cigarette bar unit, which permit further improvement of the precision of inspection, is provided. According to the method and the apparatus, the mean, variance and standard deviation are obtained statistically through a detected pressure signal, then transformation of their normal distribution into a standard normal distribution of N(0,1) where the mean with respect to the probability density function .PHI.(t) is 0 and variance with respect to thereto is 1, is obtained. And the estimation of population standard deviation with setting of a significance level is done with the value of t with respect to the probability determined solely by determining the probability in the normal distribution, thereby effecting a decision as to whether the inspected product is non-defective or defective.