Yes and no! Using an ab machine will help you to build lean, toned muscle in your core. Meaning: your abs. The actions of building up these muscles won't actually cause you to lose belly fat at the same time as you feel the burn of these workouts.
However, when you have more muscle, you naturally burn more calories because these muscles need more fuel to stay active. Combining your use of a high-quality ab machine with a cardio workout, an appropriate diet, or both, is the key to losing belly fat for most people.
The right mix of exercises, food fuel and hydration will help you build strong, defined abs and show them off!