Pressure sensitive adhesive composition and pressure sensitive adhesive sheet

A pressure-sensitive adhesive composition comprising a pressure-sensitive adhesive that comprises:

• from 40 to 95% by mass of a rubber-based resin not comprising a styrene-derived constituent unit;
• and
• a photochromic dye of a dithienylethene-based compound,
• wherein a content of the photochromic dye is from 0.40 to 8.00 parts by mass relative to 100 parts by mass of the pressure-sensitive adhesive,
• wherein the rubber-based resin comprises a polyisobutylene-based resin in which a content of the polyisobutylene-based resin is from 60 to 100% by mass in the rubber-based resin, and
• wherein the rubber-based resin comprises a polyisobutylene-based resin having a weight average molecular weight of 300,000 to 500,000 as PIB-based resin (A) and a polyisobutylene-based resin having a weight average molecular weight of 1,000 to 280,000 as PIB-based resin (B).