Provided is a two-component adhesive that includes a first composition and a second composition, in which the first composition contains: a complex derived from an organoborane and a first compound having a first group capable of undergoing an addition reaction to an isocyanate group; and as a diluent, a second compound not having a polymerizable group, the second composition containing: a third compound having an isocyanate group and a polymerizable group; and a dehydrating agent. The first composition preferably does not substantially contain a compound having a polymerizable group.