Lumia 535 Suddenly gets automatically restarted.

Hi I have NOKIA LUMIA 535DUAL SIM. I owned 1 year ago. It get suddnely restarts when I am working on it. In a day almost 10times it restarts automatically. First i have win8.1 denim on it. That time also have this problem . Now i have win10 update onit . Although win10 onit it get suddenly restart. Please help me.