SB400 WORK ON NIKON D40?

So my bulb in my flash on my d40 has gone and i was going to buy a nikon sb400 speedlight for my D40 then i was reading that it would only work on manual mode - i don't want to have to keep focusing the lense jus to use the flash - i expected it jus to work on normal autofoucs mode - will it work on autofocus mode or will i have to use my camera on manual?

Fully compatible. Both are modern Nikon systems.

Bring your D40 when you buy it and try to make sure you will understand what you are saying. I'm using SB400 on my D40 and it works great, anyway.

Manual mode meaning the mode dial on top of the camera. You can still use AF if you want to.

Set the flash to manual or Auto mode and the camera to manual mode. Set shutter speed to maximum flash sync speed (check the manual or set to 1/125s if you can't find it). Set flash and camera to the same ISO (preferably the lowest possible on the camera). Focus on the subject (of course by using AF). Check flash's recommended aperture size and set it on the camera. If the flash has a focal length setting, set it to the focal length of the lens you will be using. That's it. If you use the flash in Auto, you will get a range of distance to work on so you won't have to check the settings on the camera every time you shoot.