To provide a needle threading device for a sewing machine, which allows string to hardly come off after performing a needle threading work without requiring, especially skill for a work of an operator.

The needle threading device is provided with a needle threading shaft in close proximity to a needle bar supporting and moving a needle up and down, a needle threading hook of which the hook part can be introduced/removed into/from a needle hole, a regulation mechanism for regulating the descent limit of the needle threading shaft, and a rotation mechanism for rotating the needle threading shaft in proximity to the limit of the shaft by a specified angle so as to insert the hook part through the needle hole. The needle threading device has an needle thread lock part for keeping needle thread hooked by the hook part at a position higher than the hook part till prescribed tension is applied after pressing down the needle threading shaft by an operational body in proximity to the lower limit and rotating the operational body and inserting the hook part to the needle hole of the sewing needle, and then, cutting the useless needle thread.