If this is just for display, just use a mask. Right click on your dataframe and select advanced drawing options, go to masking and turn it on, select your polygon layer to mask with and your raster layer to be masked. If you really need the clipped raster you should just create a square polygon of the extent of your raster and then use your existing polygon to erase and hole. The use this polygon to do your clip.
Hi and thanks for replying. Okay, I got part of it [ATTACH=CONFIG]14128[/ATTACH], but after I made the square polygon, I don't quite understand exactly what to do (yes, I do want to remove that irregular polygon from the raster).