Disclosed herein is an inertial sensor. An inertial sensor 100 according to a preferred embodiment of the present invention is configured to include a plate-shaped membrane 110 on which a hole 200 penetrating in a thickness direction is formed, a mass body 120 disposed on a bottom of a central portion 113 of the membrane 110, and a post 130 disposed on a bottom of an edge 115 of the membrane 110 to support the membrane 110 and surrounding the mass body 120. By the configuration, the preferred embodiment of the present invention reduces damping force due to viscosity of air at the time of vibration by forming the hole 200 on the membrane 110 to increase displacement or amplitude of the mass body 120, thereby increasing sensitivity of the inertial sensor 100.