A breech device of a hand firearm, comprising: a firearm casing including a cross stop; a trigger mechanism including a trigger lever pivotally coupled to the firearm casing and having a stop detent; a carrier slidably arranged within the firearm casing, the carrier including a rear portion having a vertical well, and a locking arm disposed in the vertical well, the locking arm 5 pivotally coupled to the carrier with a bearing pin and including a free end that engages the cross stop, wherein the locking arm engages the cross stop when the carrier is in the locked position; a breech block slidingly arranged in the carrier and engaging the carrier, the breech block including a transfer slot along a top surface, a slidable firing pin with a striker; a spring for shifting the carrier into a locked position; characterised in that it further comprises a side wall included in the carrier, said side wall including a limiting slot theretrough; a side wall included in the breech block, said side wall having a through slot; a firing spring arranged inside the breech block for launching the firing pin towards a cartridge; a tensioning element including an oval driving part slidably engaged with the limiting slot of the carrier and a projecting part including a forward-directed nose adapted to engage the stop detent of the trigger mechanism; at least one follower pin coupled to the tensioning element and engaging the firing pin, the at least one follower pin being adapted to slide in the through slot of the breech block; and a tensioning pin anchored in the carrier and including an end part extending into the transfer slot of the breech block, the tensioning pin being configured to shift in the transfer slot engaging the back surface of the transfer slot to get the breech device in an unlocked position and the front surface of the transfer slot to lock the breech device. a firearm casing including a cross stop; a trigger mechanism including a trigger lever pivotally coupled to the firearm casing and having a stop detent; a carrier slidably arranged within the firearm casing, the carrier including a rear portion having a vertical well, and a locking arm disposed in the vertical well, the locking arm 5 pivotally coupled to the carrier with a bearing pin and including a free end that engages the cross stop, wherein the locking arm engages the cross stop when the carrier is in the locked position; a breech block slidingly arranged in the carrier and engaging the carrier, the breech block including a transfer slot along a top surface, a slidable firing pin with a striker; a spring for shifting the carrier into a locked position; characterised in that it further comprises a side wall included in the carrier, said side wall including a limiting slot theretrough; a side wall included in the breech block, said side wall having a through slot; a firing spring arranged inside the breech block for launching the firing pin towards a cartridge; a tensioning element including an oval driving part slidably engaged with the limiting slot of the carrier and a projecting part including a forward-directed nose adapted to engage the stop detent of the trigger mechanism; at least one follower pin coupled to the tensioning element and engaging the firing pin, the at least one follower pin being adapted to slide in the through slot of the breech block; and a tensioning pin anchored in the carrier and including an end part extending into the transfer slot of the breech block, the tensioning pin being configured to shift in the transfer slot engaging the back surface of the transfer slot to get the breech device in an unlocked position and the front surface of the transfer slot to lock the breech device.