PURPOSE: To easily grasp the residual of memory capacity by providing the robot control device with an output means for outputting the number of lines to be inputted to a memory from the stored capacity of the memory.

CONSTITUTION: At the end of the input of each step in a program to be inputted through a keyboard 1, a programmer depresses a return key. The number of times of depressing the return key is counted up and stored in a counter 2c as the number of input lines. If a user inputs a prescribed key on the keyboard and requests the display of the residual of memory capacity on the way of writing of a program with a comment sentence, control is transferred to a subroutine and input capacity is found out from the total number of characters in the program inputted in S1. In S2, the number of input lines is read out from the counter 2c and the number of lines to be inputted is calculated by S3. The calculated number of lines is displayed on a display 5.