A device (50) for preparing a beverage from a food substance contained in a capsule (24) by feeding a liquid into the capsule (24) provided to the device (50), said device comprising an extraction head (20) which comprises: a first and second enclosing members (10a, 10b) delimiting a receptacle (25) for enclosing a capsule (24); a closing mechanism (1) to act on at least one (10a) of the enclosing members (10a, 10b) in relative displacement of the enclosing members, between an open position of the receptacle (25) and a closed position of the receptacle (25) with the capsule positioned therein; the closing mechanism (1) further comprising a locking means (13), a lever (21) and force demultiplying means (11) for transmitting a movement of the lever (21) into the relative displacement of the enclosing members (10a,10b); wherein the demultiplying means (11) are designed to vary a transmission ratio of the closing mechanism (1) acting between the lever (21) and at least one (10a) of the enclosing members (10a, 10b).