But in front of a Murrayfield crowd of just over 8,000, Scotland rallied after the interval and John Barclay scored twice in five minutes to give the hosts a more comfortable lead.
Japan regrouped and deservedly got on the scoresheet in the final seconds through flanker Youngdae Kim, but only after Simon Danielli grabbed Scotland's fourth try in the corner just moments earlier.
But while admitting his side has room for improvement, Robinson was pleased to get in some match practice ahead of their first match against the Pumas on June 12.
He said: "It was a very good exercise, exactly what we need at this stage. The guys have been training hard, pretty intense, and we wanted to do specific things tonight, which was why I told them not to kick for the first 20 minutes.
"The contact area was a good lesson for us. The Japanese tackled very well, they went low and we weren't able to stay on our feet, and we off-loaded to them sometimes which was sloppy.
"Scott MacLeod got through and got tackled close to the line and we saw a bit of white-line fever, like we saw in the Italy game, and that's something we need to correct, but John Barclay's lines out wide were very good.
"But we are trying things. It wasn't a full-on Test match and overall I'm pleased, particularly with the simplicity of the first try.
"We stopped going forward at the breakdown after that which was why we got turned over, but we managed to improve that in the second half."