To provide an expansion tent roof device which prevents rainwater from running down from a leading end portion of a tent roof, by effectively blocking rain in a rainfall, and which does not block a passage because the front of a shop can be widely opened.

This expansion tent roof device includes: a tent roof member TY which is expanded/contracted in the state of having the leading end portion directed obliquely downward; an eaves gutter member NT which is provided at the leading end portion of the tent roof member TY; a pipe gutter member SP which communicates with rainwater lead-out portions NTp at both the ends of the eaves gutter member NT; and a downpipe member TT which downward guides the rainwater guided through the pipe gutter member SP. The pipe gutter member SP, which communicates with the eaves gutter member NT and the downpipe member TT via a rotary joint gutter member RJ, is expanded/contracted following the expansion/contraction of the tent roof member TY.