The present invention provides a terahertz-wave detection element with high spatial resolution and suitably suppressing a crack occurrence. A method of manufacturing a terahertz-wave detection element capable of detecting a spatial intensity distribution that an incident terahertz wave has includes: an oxide formation step of forming an oxide layer on one main surface of a first substrate consisting of an electro-optic crystal in which a refractive index at an incident position of a terahertz wave changes in accordance with incident intensity of the terahertz wave; a joining step of joining the one main surface of the first substrate and a second substrate by an adhesive consisting of a thermosetting resin; a polishing step of thinning the first substrate of a joined body obtained by the joining step, to a thickness equal to or larger than 1 µm and equal to or smaller than 30 µm by polishing the first substrate; and a segmentation step of obtaining a large number of terahertz-wave detection elements by cutting the joined body into pieces of a predetermined element size. In the oxide formation step, the oxide layer is formed such that the first substrate becomes convex to a side of the one main surface by causing a tensile stress to act on the first substrate.