PURPOSE: To accurately and safely detect the bobbin thread remainder with a simple structure by calculating the bobbin thread remainder of a sewing machine based on the output characteristic of an insertion quantity detecting means and the signal outputted when a detecting rod is inserted.

CONSTITUTION: When the rotating hook 31 of a bobbin thread remainder detecting device is stopped, a detecting rod 53 is inserted into a bobbin case 39 into contact with a bobbin thread 43 wound on a bobbin 45. The insertion quantity of the detecting rod 53 corresponds to the remainder of the bobbin thread 43. Various programs used for the bobbin thread remainder detection process are stored in a control circuit, and they are used after a vacant bobbin 45 wound with no bobbin thread 43 is fitted to a shuttle section before sewing is started then the preset operation and process are performed. In the bobbin thread remainder calculation process, the generated voltage VH of a hole element 61 corresponding to the insertion quantity of the detecting rod 53 is compared with the voltage VD corresponding to the preset level. If VH exceeds VD, the bobbin thread remainder is judged to be a warning level, a bobbin thread warning lamp is lighted, and a buzzer is sounded.