Looks like a little cockerel to me! How old is he? There could be a number of things going on here, but the easiest way to find out is to look at the age.
1. If this chick was laying eggs and was definitely a female, it could very well have changed genders. This can happen when the girl's ovaries stop working and she stops laying. This also causes the body to change into a cock-like state where the comb and wattles swell and she starts crowing.
2. Some hens just like to crow! It's rare, but it can happen!
3. It was thought to be a female at a young age but as it got older it turnes out to be a male.
In this situation, the bird looks rather young. So i'm going to go with option three on this one.
Although females will crow, even when there are males around. I had one do that to me. I had always heard they only did it if there was no male. No sex change for that girl. Once she got over the crowing thing she went on to raise plenty of chicks.
I had the same thing happen! For months we thought it was a crazy hen but then she sprouted up to nearly as tall as my hips and her comb got real big...and so we had a beautiful ( and huge) rooster named Saphire!