This thermocompression bonding device is provided with a heating tool (1) and a backup member (3). The backup member (3) has: a support portion (3a) which faces the tip (1a) of the heating tool (1) while first and second members (111, 122) to be joined and a cushioning member (2) are located therebetween, and which supports the first and second members (111, 122) to be joined; and a body portion (3b) provided on the opposite side of the support portion (3a) from the first and second members (111, 122) to be joined. The support portion (3a) is formed so that the heat conductivity thereof is lower than that of the body portion (3b).