Belt tensioner comprising - a base body having a bottom portion and two side walls (21, 22), - a tension lever with two side walls (30, 31), which is pivotably articulated on the base body and can be pivoted by pivoting from an unlocking position into a locking position and vice versa as well as - locking means, which are adapted to lock the tension lever in the locking position on the base body, wherein the locking means comprise - a spring element, which is arranged on the inner side of the tension lever pointing to the bottom portion in the locking position and has a first locking portion, which extends outwardly through a first side wall of the tension lever and - a first hooking groove, which is formed in a first side wall of the base body and in which the first locking portion in the locking position of the tension lever engages and is held therein for blocking an opening movement of the tension lever by a mechanic prestress of the spring element, wherein the spring element has a handling portion, to which an external force can be applied by a user, so that the first locking portion can be moved against the prestress of the spring element from the first hooking groove, wherein the spring element has a second locking portion, which extends outwardly through a second side wall of the tension lever and the locking means comprise a second hooking groove, which is formed in a second side wall of the base body and in which the second locking portion engages in the locking position of the tension lever and is held therein for blocking the opening movement of the tension lever by the mechanical prestress of the spring element, characterised in that the spring element has a first and a second spring leg (45, 46), which extend on the inner side of the handling portion of the tension lever and that on the inner side of the handling portion two counter bearings (320, 321) are provided, on which one of the two spring legs (45, 46), respectively, abuts in order to create a mechanical prestress, wherein the counter bearings (320, 321) are integrally formed with the handling portion. - a base body having a bottom portion and two side walls (21, 22), - a tension lever with two side walls (30, 31), which is pivotably articulated on the base body and can be pivoted by pivoting from an unlocking position into a locking position and vice versa as well as - locking means, which are adapted to lock the tension lever in the locking position on the base body, wherein the locking means comprise - a spring element, which is arranged on the inner side of the tension lever pointing to the bottom portion in the locking position and has a first locking portion, which extends outwardly through a first side wall of the tension lever and - a first hooking groove, which is formed in a first side wall of the base body and in which the first locking portion in the locking position of the tension lever engages and is held therein for blocking an opening movement of the tension lever by a mechanic prestress of the spring element, wherein the spring element has a handling portion, to which an external force can be applied by a user, so that the first locking portion can be moved against the prestress of the spring element from the first hooking groove, wherein the spring element has a second locking portion, which extends outwardly through a second side wall of the tension lever and the locking means comprise a second hooking groove, which is formed in a second side wall of the base body and in which the second locking portion engages in the locking position of the tension lever and is held therein for blocking the opening movement of the tension lever by the mechanical prestress of the spring element, characterised in that the spring element has a first and a second spring leg (45, 46), which extend on the inner side of the handling portion of the tension lever and that on the inner side of the handling portion two counter bearings (320, 321) are provided, on which one of the two spring legs (45, 46), respectively, abuts in order to create a mechanical prestress, wherein the counter bearings (320, 321) are integrally formed with the handling portion.