A cutting device for a sewing machine includes an upper-blade positioning device and a lower-blade positioning device. The upper-blade positioning device includes an upper blade upper blade fixed at a head portion of the upper-blade holder, and a spring and a restricting member sleeved on a body portion of the upper-blade holder. A restricting pin is engaged between an upper-blade drive member and the restricting member. A guide member includes a guide hole for insertion of a rod portion of the upper-blade drive member and is fixed to the base. The upper-blade drive member is inserted through a guide member of the base and moved by a connecting rod. The lower-blade positioning device includes a lower-blade holder, an adjustment member. A lower-blade shaft has one end fixed to the base and another end extended out of the base, rotating the adjustment member can adjust the position of the lower-blade holder.

An overlock sewing machine includes a first switching part for switching an interlocked state where an upper knife drive part and an upper knife are interlocked and a released state where the upper knife drive part and the upper knife are not interlocked; a second switching part for switching the upper knife between a projection position and a retreat position; and an operation part for switching the first switching part and the second switching part between a first mode, a second mode, and a third mode.

A sewing machine includes a sewing machine motor configured to generate drive power to drive a needle bar up-and-down motion mechanism and a cutting unit. The cutting unit includes a cutting needle having a distal end with a blade, and a cutting needle up-and-down motion mechanism having a first motor separate from a sewing machine motor and configured to generate drive power to move the cutting needle independently of the needle bar up-and-down motion mechanism. A cut is formed by the blade as a result of up-and-down motion of the cutting needle while the cutting needle is held in a manner such that an extending direction of the cutting needle corresponds with an extending direction of the needle bar. The cutting unit further includes a cutting needle rotating mechanism configured to rotate the cutting needle about a central axis line of the cutting needle directed to the extending direction.