Vertical drain trap

The present invention provides a vertical drain trap that is easy to maintain and compact. The vertical drain trap (X) includes: A main body casing (1) has an inflow pipe part (11) for liquid inflow, a discharge pipe part (12) for liquid discharge along the up and down direction, and the valve casing (13) located between the inflow pipe part (11) and the discharge pipe part (12). A valve unit (2) has a valve body (21) capable of contacting the valve seat (11b1) formed on the inflow pipe part (11) from the lower side, a magnet mechanism (23) for moving the valve body (21) upward, and a guide member (22) that guides the movement of the valve body (21) under the weight of the liquid and the movement of the valve body (21) caused by the magnet mechanism (23). The valve unit (2) is mounted in the valve casing (13). An opening (13A) from which at least the valve body (21) and the magnet mechanism (23) in the valve unit (2) can be taken out is formed in the valve casing (13) from a direction intersecting with the up