Provided are a displacement detector, a surface shape measuring apparatus, and a roundness measuring apparatus capable of measuring displacement in a plurality of directions, having a simple configuration, and capable of highly accurate measurement. A displacement measurer includes: a detector body; a substantially L-shaped stylus having a contactor to be in contact with a measuring surface of an object to be measured; a stylus holding part that is provided in the detector body and holds the stylus in a swingable manner, with a swing plane being a plane including a first direction and a second direction that are perpendicular to each other; and a displacement detecting unit that is provided in the detector body and detects displacement of the contactor associated with contact between the contactor and the measuring surface.