Problem with shadows

Hello everyone and thank you in advance for your help,

I have a problem of shadows in Unity, I have triangles (shadow) on a face that should not have shadow, a face exposed to the sun (directional light). Here is a picture with a lot of details.

Have you ever seen that? How can I fix that? I tried a lot of things but I did not find a solution, is this a scale problem?

thanks again,
Sorry for my english not very good
Nathanaël

UP! :wink: