(57) To provide a collection method capable of collecting ε-caprolactam and a polyamide 6 oligomer in high yield only by depolymerization using a small amount of water and solid-liquid separation with a small energy consumption. The present invention is a method for collecting ε-caprolactam and a polyamide 6 oligomer, including adding a resin composition (A) containing at least polyamide 6 and at least one of water (B) heated to 290°C or higher and 350°C or lower and a polyamide 6 oligomer aqueous solution (B1) heated to 290°C or higher and 350°C or lower to make contact with each other to obtain a reaction mixture (C) containing at least ε-caprolactam, a polyamide 6 oligomer, and water, and subjecting the reaction mixture (C) to a solid-liquid separation (I) in a temperature range not higher than a boiling point of water at an operation pressure to separate and collect a polyamide 6 oligomer in a solid phase, and an ε-caprolactam aqueous solution in a liquid phase.