A detection device of a substance to be measured according to an embodiment of the present disclosure is intended to conveniently detect a bio-related substance such as a bacteria or a fungus. The detection device according to an embodiment of the present disclosure includes, a container that contains solution and a composite particle combining a substance to be measured and a magnetic labeling substance, a magnetic field applying unit that applies a magnetic field to a predetermined region so as to collect the composite particles, wherein spatial light is incident to the predetermined region other than lower region of the container, an imaging unit for imaging the composite particles collected in the predetermined region where the spatial light is incident, a detection unit that detects the composite particles based on the image captured by the imaging unit.