PURPOSE: To provide a method for manufacturing a battery diaphragm having small internal resistance within an actual using temperature range and high safety in the case of abnormality such as outside short-circuiting.

CONSTITUTION: A method for manufacturing a diaphragm comprises a process of soaking a part of a rotatable roll 2 into resin dispersed liquid 5 so as to coat an application surface 2a of the roll 2 with the resin dispersed liquid while rotating in the fixed direction; a process of feeding out a diaphragm main body 6 made of a porous resin subjected to a hydrophilic treatment at a fixed speed in such a manner as to be brought into contact with the application surface 2a of the rotating roll 2 under a fixed pressure; and a process of transferring the resin dispersed liquid adhering to the application surface 2a of the roll 2 onto a surface 6a of the diaphragm main body 6 so as to continuously apply a resin dispersed liquid layer 9 of a fixed thickness onto the surface 6a of the diaphragm main body 6.