A firing linkage mechanism (F) includes a hammer (1) for striking a firing pin (15) against an air plug (2) in a submachine gun, a bolt (3) mounted inside the gun body (A) of the submachine gun above a magazine holder (A1), a counterweight set (4) pivoted to the rear side of the bolt (3) and movable downwardly along oblique sliding rail portions (C2) of sliding rails (C) in the gun body (A), a side frame bar (21) affixed to the magazine holder (A1), a link (22) pivotally coupled between the side frame bar (21) and the firing pin (15) and biasable forwardly following a forward displacement of the firing pin (15) and the air plug (2) upon striking of the hammer (1) against the firing pin (15) and forcible to return the firing pin (15) and the air plug (2) after the striking action of the hammer (1), and a stop rod (23) for engaging the link (22) to hold the link (22), the firing pin (15) and the air plug (2) in position and to stop the link (22) from returning the firing pin (15) and the air plug (2) after the striking action of the hammer (1) and movable by the counterweight set (4) to release the link (22) for stopping the compressed gas from flowing out of the magazine (B) into the bolt (3) when the counterweight set (4) is moved along the oblique sliding rail portions (C2) of the sliding rails (C) in the submachine gun.