A physical quantity sensor according to the embodiment includes: a substrate; a movable body including a movable electrode portion; and a support which supports the movable body around a first shaft to be displaced, in which, when the movable body is divided into a first portion and a second portion with the first shaft as a boundary, the physical quantity sensor includes a first fixed electrode portion which is disposed on the substrate to oppose the first portion, and a second fixed electrode portion which is disposed on the substrate to oppose the second portion, and a guard portion which suppresses an electrostatic force generated between the movable body and the substrate is provided in an inter-electrode area between the first fixed electrode portion and the second fixed electrode portion, on the substrate.