A linkage assembly is provided for guiding movement of a key cap relative to a support board. The linkage assembly includes left and right modular linking members, and a pair of synchronizing units each including a left upper cavity, a left lower cavity, a right upper cavity, and a right lower cavity. In a normal position of the key cap, a left downward abutment region of the left lower cavity is in frictional engagement with a right upward abutment region of the right upper cavity. In a pressed position of the key cap, a left upward abutment region of the left upper cavity is in frictional engagement with a right downward abutment region of the right lower cavity.