the present invention provides a thermally expandable microcapsule that has a high expansion ratio and durability at high temperatures , and is not likely to cause discoloration and odor when used for foam molding . the thermally expandable microcapsule of the present invention includes : a shell formed from a polymer ; and a volatile expansion agent as a core agent encapsulated by the shell , the shell obtained by polymerizing a monomer composition that contains a nitrile monomer and a compound having a glycidyl group in a molecule , the shell exhibiting a value y of 50 % or higher and a ratio y / x of 1 . 1 or higher , in which x represents a gel fraction at ordinary temperature , and y represents a gel fraction upon heating at 180 ° c . for 30 minutes .