An acetylated softwood lignin fiber having a diameter of 5 to 100 microns. The occurrence of solder bridges between the terminal electrodes during solder mounting and the occurrence of chipping in the terminal-electrode-forming areas between the recesses on the lengthwise sidewall are both reduced by making the width of the recesses along the lengthwise sidewall either 0. If the data bits are unbalanced by a specified amount, a portion of the bits on the data bus are inverted, and the data bits, including the inverted portion, are transmitted. Processing of the interrupt can be executed by the one load module even during the rebooting of the operating system. The fastening mechanism includes a group of claws formed on the inner circumference of the first piece cylindrical part and a group of claws formed on the outer circumference of the second piece cylindrical part.