saranyootiwutanon,
On behalf of Tom's Moderator Team, welcome aboard!
At the top of all our Forums you'll see "Stickies" which are Threads that are permanently "stuck" in place, and are reference information posted for everyone's benefit. Near the top of the CPU's Forum you'll see a Sticky you might want to read:
Intel Temperature Guide -
http://www.tomshardware.com/forum/id-1800828/intel-temperature-guide.html
The short answer to your question is yes, 75°C is OK.
Here's the operating range for Core temperature:
Core temperatures above 85°C aren't recommended.
Core temperatures increase and decrease with Ambient temperature.
Highest Core temperatures occur during...