As John says plus it's probably somewhat rusted around the center part of the axle. Providing you have a 1/2 ton truck. Spray some penetrating oil around the axle flange, back off the adjusters, tap the drum and it should come off.
Fred

1956 3100 Pickup/Red/350/3sp OD/PS/Disc Brakes
1957 Bel Air Sport Coupe/Red/355/TH350/PS/Disc Brakes
2017 Silverado LT Single Cab SB/Black/5.3/6 Speed Trans
1947 Willys CJ2A w/F-Head engine