Why are the bones changing the mesh s size while the animation is going?

Hello everybody!My problem is : After I gave bones to my charachter,and I made an animation for it, the bones always changin my charachter;also I put a sword in it s hand ,and the sword is flying off when the animation is playing,I set up everything(like parenting,etc.)but I can t slove it. Please Help! here is the .blend file : https://www.mediafire.com/?h7x8e6t7tp7y45t