To provide a tackifier which is transparent, hardly generates deterioration reaction by UV and the like and has excellent compatibility with a styrenic block copolymer, and to provide an adhesive composition having excellent light resistance, hardly deteriorated even when exposed to UV and the like for a long time and having the styrenic block copolymer having excellent transparency as a base resin.

The tackifier for styrenic block copolymer contains an esterified product (A) of rosins having the maximum absorbance A (measurement condition: sample concentration 1 g/dm3, cell length 1 cm) in ≥254 nm region by a UV absorption spectroscopy of 0.15 or below and having ≥95% content of a component having a molecular weight of 320 measured by gas chromatograph mass spectrometry of methylation treatment product of a hydrolyzed product to sum total content of component having molecular weight of 314 to 320.