Thread tension adjusting device for a sewing machine

An adjusting device for a sewing machine having an arm for accommodating said adjusting device, said adjusting device comprising a casing fixed in said arm of said sewing machine, an axle rotatably supported in said casing and having a first end extended outward of said casing, a shaft fixed in said casing in parallel with said axle, a knob fixed to said first end of said axle and extended outward of said arm of said sewing machine, at least one cam fixed on said axle, a lever having a first end pivotally fixed on said casing and having a second end slidably engaged on said shaft and having a protrusion formed on a middle portion thereof for slidably engaging said cam, and a gripping device disposed beside said second end of said lever and including a pair of members, one of said pair of members being fixedly secured to said shaft and the other member being slidably engaged on said shaft and means disposed between said second end of said lever and said pair of members for biasing said pair of members together so that a thread is gripped between said pair of members, and when said second end of said lever is moved toward or moved away from said pair of members when said axle and said cam are rotated, a tension force applied to said thread is adjusted.