its needle bed and with a needle pitch sensor 43 in parallel with the needle bed 41 there is disposed a needle pitch indicating member 44 which is located by the needle pitch sensor 43 made to reciprocate with the movement of the carriage the needle pitch indicating member 4 is formed with marks 45 and 46 for determining the range of measurement of the yarn length for the later described yarn length measurement indicated at numerals 47 and 48 are feeders which are identical to such well known mechanism as can move together with the carriage 42 in accordance with the movement of the carriage 42 while being retained on the carriage 42 numerals 49 and 50 indicate pulse encoders for yarns 51 and 52 and numerals 53 and 54 indicate packages for yarn feed sources in the embodiment thus far described the yarn feed sources 53 and 54 and the pulse encoders 49 and 50 are arranged at both the lefthand and righthand sides of the machine frame but it is quite natural that they may be disposed only at one side of the machine frame the pulse encoders 51 and 52 are used to measure the lengthes of the yarns and to generate one or a predetermined number of pulses for each rotation and their signals are fed to an encoder control unit 61 the output of the needle pitch.