The image shows a wooden structure on wheels, with a large, pointed log attached to ropes and a frame. There are also smaller figures (likely representing people) positioned to turn wheels attached to axles that wind the ropes.
Step 2: Consider the options
Siege tower: A tall, mobile structure used to scale walls. This isn't a tower.
Trebuchet: A large catapult that uses a counterweight. This device lacks the characteristic arm and counterweight.
Catapult: A device that launches projectiles. This image fits this description.
Battering ram: A heavy beam used to break down walls or gates. This is not a battering ram.