To provide a connection device of a toilet bowl and a drain pipe, which does not disturb shape configuration as a molding and suppresses the occurrence of deformation and breakage caused by a load and a high temperature produced during cutting work.

A connection device of a toilet bowl and a drain pipe is used for connecting an outlet part of a drain pipe of a toilet bowl body of a flush toilet bowl to an inlet part of an underfloor drain pipe installed under a floor. The connection device includes: a toilet bowl body side connection pipe member connected to the outlet part of the drain pipe of the toilet bowl body; a drain pipe side connection pipe member connected to the inlet part of the underfloor drain pipe; and an intermediate pipe member connecting the toilet bowl body side connection pipe member and the drain pipe side connection pipe member to each other and extending substantially linearly. A reinforcement member is provided continuously in the longitudinal direction of the intermediate pipe member. Thereby, the occurrence of deformation and breakage caused by a load and a high temperature produced during cutting work can be suppressed.