Tax was about 14% this month. Is that normal? Part-time job. Also Main vs. Secondary tax

Hello! I have emailed my employer my tax questions, but they're closed for the day.

I'm a bit confused about monthly taxes. I work part-time so my income with this company varies each month. This month my gross income was about 290k and I was taxed 40k, about 14%. Last month my pay was a lot less due to Obon so I think it was only around 2k (about 5% of what I made that month?). The last pay with this company that was about 200k was about 10%. Does it vary that much when you're part time? Does this seem right?

Another bit of info is for some reason they've listed secondary tax when they were supposed to be main. I don't know what the difference is so I'm not sure why there's two. I did try googling it in English but I haven't tried Japanese yet. Not sure if that affects it?

I don't have my tax statements from my last full time job, so I can't compare them to this years'. I just ended up with a bit less than I expected cuz I didn't calculate this.