A trocar apparatus includes a trocar and a trocar shaft. The trocar has a retractable-type camera section and a seal unit. The seal unit has a dome type seal and a first mount. A step is formed on the proximal side of a puncture member at the distal end of the trocar shaft. A relationship between a puncture member length L1 of the puncture member and an interval L2 in the axial direction of the trocar from the boundary position between a pipe section and a head section to a first mount opening satisfies conditional formula (A) given below:L1>；L2 ； ；(A).
