Strange Pro Shadow

Hello.

My Unity pro 4.2.2f1 has unknown strange phenomenon.
Why, I do not know whether the appearance is bad as this.

This is Directional light setting.

RenderSettings
1392087--71633--$r.png

OS:Mac 10.7.5 Lion

Could you help me?
Thanks in advance.

Resolution under light tab is set to low res. change the shadow type to Soft, and resolution to very high.

Also, increase the bias.

–Eric

Thank you everyone!
I fix now!