To provide a filter said to be a base filter having a water pumping-up cylinder mounting part having an upper wall and the peripheral side wall falling from the peripheral edge part thereof and provided with water passing holes in a dispersed state, preventing gravel from entering its internal space at maintenance on the like, used as it is in such a state that gravel is present on the downstream side of the filter and capable of being simply and easily subjected to maintenance work or the like.

The filter A includes a filter body 1 having the upper wall 11 and the peripheral side wall 12 falling from the peripheral edge part of the upper wall 11 and the lid body 2 for closing the lower end openings 13 of the filter body 1. The filter body 1 has the upper wall 11 and the peripheral edge part 12, and they keep a large number of filtering water passing holes 111 and 121 dispersed with the water pumping-up mounting part 15 carried by the upper wall 11.