Disclosed herein are a crystal comprising a compound, which has μ-opioid receptor antagonistic action, few side effects, and high safety, and having high purity and excellent physical properties (stability, solubility, etc.), and a method for producing the crystal.The crystal is a crystal of a salt comprising: a compound represented by a formula (I)[wherein R2 is a hydrogen atom or a halogen atom, and R1 is a group selected from the group consisting ofand an acid selected from the group consisting of hydrochloric acid, hydrobromic acid, and oxalic acid, or a hydrate thereof.
