Take the shuttle elevator to the 24th floor then follow the signs for the elevator hall where you can take the elevator to the 38th floor.
Access
Roppongi 1-chome Station (Tokyo Metro Namboku Line) direct access
Tameike-Sannou Station (Tokyo Metro Namboku Line, Ginza Line) 7 minutes from Exit 13
Kamiya-cho Station (Tokyo Metro Hibiya Line) 7 minutes from Exit 2