Intended is to provide a fine bubble-diffusing pipe capable of producing fine bubbles efficiently uniformly and homogeneously even if a diffusing pipe is elongated, and a fine bubble diffusing device and a dipped type film separating device using the fine bubble diffusing pipe. This fine bubble diffusing pipe comprises a cylindrical support pipe (1), and an elastic sheet (2) having fine slits formed therein. The elastic sheet (2) is arranged to cover the outer circumference of the support pipe (1). When the clearance between the elastic sheet (2) and the support pipe (1) is fed with a gas, the fine slits of the elastic sheet (2) are opened to perform the function to produce the fine air bubbles to the outside of the diffusing pipe. The fine bubble diffusing pipe is characterized in that the support pipe (1) has a longitudinal length (L) of 1,000 mm or more, and in that the support pipe is equipped at its two ends with gas feed portions (4) acting as gas inlet ports.