The thermosetting resin composition according to the present invention includes a resin (A) containing two or more carboxyl groups and having a polyurethane structure, a strongly basic nitrogen-containing heterocyclic compound having pKa of 10.0 to 14.0 as a curing accelerator (B) and a curing agent (C). A cured product of the thermosetting resin composition is used as an insulating protective film for printed wiring boards, flexible printed wiring boards, chip-on-films, etc. The thermosetting resin composition of the invention has improved low-temperature curability and instantaneous curability, can realize tack-free property, can simultaneously realize low warpage property and electrical insulation property, does not contaminate a curing oven and the like by outgassing during heating, has a sufficient pot life, can form excellent cured products and insulating protective films, and can form solder resists and insulating protective films at low cost with good productivity.