An eyewear device which adjusts a transmitted light amount to a left eye and a right eye of a viewer to perform an assistance operation, which assists the viewer in viewing images so that the viewer stereoscopically perceives the images, comprising: a receiver configured to receive a synchronization signal in synchronization with display of the images; and a controller which analyzes a signal configuration of the synchronization signal after power supply is started for the assistance operation, and switches a control mode between a first control mode and a second control mode, which is different from the first control mode, based on an analysis result of the signal configuration.