Membrane heat treatment method

A membrane heat treatment method for heating a membrane having small pores with adsorbates adsorbed therein, the membrane heat treatment method comprising:

• a) raising a temperature of the membrane to an intermediate heating temperature;
• b) heating and keeping said membrane at said intermediate heating temperature for a predetermined period of time;
• c) raising the temperature of said membrane to a main heating temperature that is higher than said intermediate heating temperature;
• and
• d) heating and keeping said membrane at said main heating temperature for a predetermined period of time,
• wherein a first recovery amount that is a difference in permeability of said membrane between after said operation b) and before said operation a) is 50% or more and 95% or less of a second recovery amount that is a difference in permeability of said membrane between after said operation d) and before said operation a).