A thread cutting device for a sewing machine comprising: a cutting knife including a cutting edge and serving to carry out a rotation to an initial position and a thread cutting position advanced from the initial position to a stitch point side; a moving knife rotated to the initial position, a thread catching position advanced from the initial position and the thread cutting position retreated from the thread catching position in order and serving to cut a bobbin thread and a needle thread in cooperation with the cutting knife in the thread cutting position; and a clamp member for interposing and holding the bobbin thread between the clamp member and the moving knife by an elastic force applied through an elastic deformation, the clamp member including a first interposing portion for interposing the bobbin thread between the first interposing portion and the moving knife when the moving knife is returned from the thread cutting position to the initial position, wherein the moving knife includes a catching portion for catching the bobbin thread in the thread catching position, characterized in that a guide groove is formed on an inside face of the moving knife, which is opposed to the clamp member, wherein the clamp member includes a second interposing portion for interposing the bobbin thread in abutment on a first abutting portion provided on a tip side of the moving knife from the catching portion when the moving knife is placed in the thread cutting position, and wherein the bobbin thread interposed by the second interposing portion in the thread cutting position is transferred to the first interposing portion and is held by the first interposing portion with a movement of the moving knife to the initial position, and wherein one end of the moving knife is linked to the catching portion of the moving knife and the other end of the moving knife is placed on a tip end side of the moving knife from the one end in an inner side face of the moving knife opposed to the clamp member. a cutting knife including a cutting edge and serving to carry out a rotation to an initial position and a thread cutting position advanced from the initial position to a stitch point side; a moving knife rotated to the initial position, a thread catching position advanced from the initial position and the thread cutting position retreated from the thread catching position in order and serving to cut a bobbin thread and a needle thread in cooperation with the cutting knife in the thread cutting position; and a clamp member for interposing and holding the bobbin thread between the clamp member and the moving knife by an elastic force applied through an elastic deformation, the clamp member including a first interposing portion for interposing the bobbin thread between the first interposing portion and the moving knife when the moving knife is returned from the thread cutting position to the initial position, wherein the moving knife includes a catching portion for catching the bobbin thread in the thread catching position, characterized in that a guide groove is formed on an inside face of the moving knife, which is opposed to the clamp member, wherein the clamp member includes a second interposing portion for interposing the bobbin thread in abutment on a first abutting portion provided on a tip side of the moving knife from the catching portion when the moving knife is placed in the thread cutting position, and wherein the bobbin thread interposed by the second interposing portion in the thread cutting position is transferred to the first interposing portion and is held by the first interposing portion with a movement of the moving knife to the initial position, and wherein one end of the moving knife is linked to the catching portion of the moving knife and the other end of the moving knife is placed on a tip end side of the moving knife from the one end in an inner side face of the moving knife opposed to the clamp member.