PURPOSE: To provide a detachment prevention device having the capability of preventing an embroidering attachment detachably mounted on a base plate from being separated at the time of carrying a sewing machine.

CONSTITUTION: A synthetic resin lock member 20 is projected from an embroidering attachment 1 in a mounting direction, and an engagement claw section 20a projected down is formed at the end of the member 20. Also, an engagement hole 22 is drilled through the wall section of a base plate where the engagement claw section 20a of the member 20 is in slidable contact. The attachment 1 is prevented from being separated by coupling the section 20a to the hole 22. On the other hand, a horizontal link 26 with one end capable of engaging with the lower side of the lock member 20 is so supported on the attachment 1 at an intermediate section as to be rotatable, and a vertical link 24 fixed to an operation button 23 is connected to the other end of the link 26. The engagement claw section 20a is detached from the hole 22 by pressing the operation button 23.