压缩机（英语：Gas compressor），是一种将气体压缩并同时提升气体压力的机械，其应用广泛，常见的应用领域包括：暖通空调、冷冻循环、提供工业驱动动力、硅化工、石油化工、天然气输送等。

依据其运作原理，可分为容积式压缩机（或称置换式，英语：positive-displacement）与气体动力式压缩机（英语：aerodynamic）：

容积式压缩机乃是将气体导入一密闭空间中，透过压缩原有气体所散布的空间体积而使内部压力上升，而将机械能转换为压力能。依据其压缩方式的不同，又可分为往复式、回转式、涡卷式、螺旋式等。

A gas compressor is a mechanical device that increases the pressure of a gas by reducing its volume. An air compressor is a specific type of gas compressor.

Compressors are similar to pumps: both increase the pressure on a fluid and both can transport the fluid through a pipe. As gases are compressible, the compressor also reduces the volume of a gas. Liquids are relatively incompressible; while some can be compressed, the main action of a pump is to pressurize and transport liquids.