In a keyboard apparatus, a key unit has one or more key bodies, a key supporting part for supporting each key body, and a connecting part for connecting the key body to the key supporting part pivotably in a key-stroking direction of the key body. A key frame has an upper surface, and a key mounting part disposed on the upper surface for mounting the key supporting part of the key unit. The key supporting part of the key unit has a first engagement section having a hook-like structure or a press-fitting structure. The key mounting part of the key frame has a second engagement section which engages with the first engagement section when the key unit is mounted to the key frame. The second engagement section has a through-hole or a concave for engagement with the hook-like structure or the press-fitting structure of the first engagement section. The first engagement section and the second engagement section are located above the key mounting part of the key frame.