In the control of a multi-joint robot main body, it is necessary to execute intricate track calculations and synchronous operations in parallel, even if the track calculations are intricate and times required for the calculations are indefinite. For this purpose, a robot controlling device of the present invention includes a shared memory, and first and second processing units connected to the shared memory. The first processing unit performs track calculation processing which includes calculating operation command data indicating a series of command values to be output to arm motors, based on a command to operate the multi-joint robot main body to a desired position posture, and storing the calculated operation command data in the shared memory. The second processing unit performs synchronous processing which includes acquiring the operation command data stored in the shared memory, and synchronously outputting the command values to the arm motors at predetermined time intervals.