Provided a terahertz-wave detection element with high spatial resolution and suppressing a crack occurrence. A method of manufacturing the detection element capable of detecting a spatial intensity distribution of a terahertz wave includes: a step of forming an oxide layer on one main surface of a first substrate consisting of an electro-optic crystal; a step of joining the one main surface of the first substrate and a second substrate by an adhesive consisting; a step of thinning the first substrate of a joined body, to a thickness of 1-30 μm by polishing the first substrate; and a step of obtaining a large number of terahertz-wave detection elements by cutting the joined body. 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 it.