To attain bobbin thread-remaining amount-detecting device of a sewing machine which is capable of detecting the remaining amount of the thread wound at a bobbin stored in a shuttle hook of a sewing machine more suitably.

With a decrease in the amount of a bobbin thread wound at the axial part 2 of a bobbin 1, the light output from a light emitting part 11 of a first detecting part 10 comes to be able to transmit the axial part 2. When a transmitted light receiving part 12 of the first detecting part 10 comes to be able to receive the light, a bobbin thread remaining amount detecting device 100 of a sewing machine switches from the first detecting part 10 to the light detecting motion of a second detecting part 20. Also, the bobbin thread remaining amount detecting device 100 of the sewing machine enables a suitable bobbin thread management so that the bobbin thread remaining in the bobbin 1 or in the shuttle hook of the sewing machine 70 which stores a bobbin 1 is not too much or too little by stopping the sewing motion of the sewing machine when it judges the rotation stop of the bobbin 1 based on the detection of a reflected light which is received by a reflected light receiving part 22 in the second detecting part 20.