To provide a motor unit mounting device of an electric solar radiation shielding apparatus that can stably hold a motor unit while facilitating mounting of the motor unit on a rail.

In a shielding material transfer device of an electric solar radiation shielding apparatus; pulleys are each rotatably supported on transfer devices which are installed at both ends of a rail; a motor unit is installed in either one of the transfer devices to rotatably drive the pulleys; and runners are transferred along the rail with a belt transferred on the basis of the rotation of the pulleys. In mounting members which are each installed in the motor unit and the transfer devices, there are provided: a hanging means for hanging and supporting the motor unit on the transfer device by turning the motor unit in a state engaged with each other; and a stopper device 52 for automatically preventing the turning of the motor unit, with the motor unit hung and supported on the transfer device.