To provide a planet gear type speed change device capable of reducing its production cost and saving its floor space by simplifying its structure.

In a planet gear type speed change device providing 6 forward speed stages advancing and one back speed stage, the planet gear section 2a of the planet gear mechanism 2 corresponding to a clutch line C3 for third and fifth speed stages is constituted into two stages, and power is transmitted between the ring gear 2b of the mechanism and the ring gear 3b of the planet gear mechanism 3 corresponding to a clutch line C2 for second and sixth speed stages adjacent to the ring gear 2b and between the ring gear 5a of a planet gear mechanism 2 and the ring gear 5b of the planet gear mechanism 3 corresponding to a clutch line C2 for second and sixth speed stages adjacent to the ring gear 2b.