A keyboard device includes key units each including keys arranged in a right and left direction, hinges, a common mounting portion which are molded in one piece. The common mounting portion is elongated in the right and left direction. Bach hinge is provided between the common mounting portion and the key. The key units include a particular key unit having an uppermost one of the common mounting portions. At least one of the hinges of the particular key unit includes a hinge thick portion connected to a rear surface of the key; and a hinge thin portion connected to a rear surface of the hinge thick portion and connected to a front surface of the uppermost common mounting portion. A protrusion protruding outward is provided on at least one of opposite outer ends of the hinge thick portion in the right and left direction.