PURPOSE: To easily obtain a desired grading density in matching with the recording characteristics of a recording paper, by storing a signal corresponding to the recorded density in advance in a memory.

CONSTITUTION: An analog signal to be recorded is applied from an input terminal 1 at a specified level and the inputted analog signal is sequentially converted into a digital signal with a clock of a specified frequency generating circuit 3 at an A-D cnverter 2. After interference and noise are eliminated from this digital signal at a digital signal processing circuit 4, the result is applied to an upper-order address of a memory 6. On the other hand, an address counter 5 repetitively designates a lower-order address of the memory 6 with an output clock of the circuit 3. Thus, a group address of the memory 6 storing a signal corresponding to the recording density in advance at each group is designated, and the designated content of storage is repetitively read out. The signal read out is amplified to a voltage required at an amplifier 7 and applied to a recording pen.