There is provided an electric keyboard assembly having a construction which is capable of reducing a height of a keyboard and at the same time facilitating key scaling to key-touch response while maintaining the degree of freedom in designing the keyboard. A key is pivotally moved by a key depressing operation. A seesaw-type mass member having a front extension and a rear extension each extending from a pivot-receiving portion thereof, and a tone-generating position adjustment screw fitted in the front extension is pivotally moved about the pivot-receiving portion by a driving force generated by depression of the key and received via the tone-generating position adjustment screw. The front extension of the mass member pops up to a level higher than the key when the key is depressed. A front weight and a back weight are arranged separately in the front extension and in the rear extension, respectively. A distance between the pivot-receiving portion and the front weight arranged in the front extension is set to be shorter than the distance between the pivot-receiving portion and the back weight member arranged in the rear extension.