To provide a technology capable of changing at least one of two letters or more of characters or figures or signs by a few input frequency.

An operation panel 21 is provided with a 7-segment display 22 for displaying at least one of the characters or the figures or the signs stored by a RAM by horizontally juxtaposing a plurality, and an operation button unit 23 arranged on the operation panel 21 and changing at least one of the characters, the figures and the signs displayed on the 7-segment display 22. The operation button unit 23 comprises a left bottom 23d and a right button 23c juxtaposed in the horizontal direction for selecting at least one position of the characters, the figures and the signs displayed on the 7-segment display 22 and tried to be changed, an upper button 23a and a lower button 23b juxtaposed in the vertical direction for changing at least one of the characters, the figures and the signs selected by the left button 23d or the right button 23c.