Apparatus having a solid-liquid separating function, mu-TAS devices and solid-liquid separation method

In a device having a solid-liquid separation function, a solid-liquid mixture is introduced through a lid inlet formed in a lid, a separation portion for solid-liquid separation is formed in a groove portion, and solid trapping portions are arranged in the separation portion. Each solid trapping portion is formed of a partition wall and includes an inlet portion, an accommodating portion which accommodates one or more solids that have entered through the inlet portion, and an opening portion which is formed on a downstream side of the accommodating portion and prevents the solid having a fixed size or larger from passing therethrough. A width of a region of the separation portion where the solid trapping portions are formed is narrow on a downstream side compared to on an upstream side.