Abstract: [PROBLEM] To provide an object lens such that the degradation of the optical properties of the object lens due to temperature change can be minimized, and a light pickup device using the same. [SOLUTION] An object lens R has lens surfaces R1, R2 which converges BD light, DVD light and CD light with prescribed numerical apertures into spots, and an antireflective film R1a formed on the lens surface R1. The lens surface R1 includes a BD exclusive region A1, a two-wavelength common region A2, and a three-wavelength common region A3. Diffractive structures P1, P2 and P3 are formed respectively for the BD exclusive region A1, the two-wavelength common region A2 and the three-wavelength common region A3. The antireflective film R1a is designed such that the transmittance for BD light is largest in the range of the two-wavelength common region A2.