PURPOSE: To obtain the subject device useful for measuring the size of raw silk capable of holding a gauge type size sensor with a balancing bar having an operating part, a reactional part and an eccentric load, sensing a change in the eccentric load corresponding to the size of the raw silk and automatically controlling the size information.

CONSTITUTION: A slit 2 at one end and a terminal 5 at the other end are installed with a supporting shaft 3 of a gauge type size sensor 1 as the center and the terminal 5 is brought into contact with a pedestal 6 supported by fulcra (9a), (7a) and (7b). The pedestal 6 is held by a balancing bar 8 supported by a fulcrum (9b) and a supporting part 10 so as to enable the free tilting. The balancing bar 8 has the pedestal 6 at one end and an operating part 13 at the other end. A reactional part 14 is further attached adjacently to or in contact with the operating part 13 and an eccentric load 11 is further attached to the balancing bar 8. The measurement is started by passing a current through a solenoid 15, attracting a movable iron core 16 and making the turning of a sensor 1 free. A change in the eccentric load 11 corresponding to the size of raw silk is made to correspond to the tilt of the balancing bar 8 of the sensor 1. The tilt is then transmitted to the operating part 13 and the reactional part 14 to measure the size of the raw silk in reeling the yarn.