A valve actuator is a valve actuator that drives opening and closing of a poppet valve and includes a motor and a transmission mechanism that transmits a drive force of the motor to the poppet valve. The transmission mechanism includes a booster mechanism. The booster mechanism is a three-dimensional toggle mechanism that includes a cylinder, an input disc that rotates about an axis in the cylinder, an output disc that reciprocates along an axial direction in the cylinder, and a link that connects the input disc and the output disc.