A display method and apparatus for navigation system for specifying the destination easily and quickly. The image forming unit may include a controller to combine color lookup tables of the two or more selected image modes and to create a new color lookup table, and an engine unit to perform the image forming job in an image mode corresponding to the new color lookup table. A network infrastructure device receives the communication and transmits, as a common channel signal during the pre-determined time, a signal with the presence information. The student’s terminal 1 has a PC 31 as a lesson device, together with a TV monitor 36, a terminal 34, etc. The collet and cutting tool shank can be drawn from the tool holder by applying rotational torque to the lock nut.