The present invention provides a composition that exhibits excellent adhesive properties to tooth structure (particularly dentin) when applied as a dental material. The present invention is a composition containing a polymerizable monomer (A) having an unconjugated carbon chain with at least four carbon atoms bonded continuously, at least two polymerizable groups, and at least two hydroxyl groups, and a bisacylphosphine oxide (B) represented by the following formula (1):
where the respective symbols are as defined in the specification.
