noun
pencil case; pencil box; writing brush case
A container for writing implements, traditionally for calligraphy brushes but now commonly used for pencils and pens.
筆箱に鉛筆と消しゴムを入れている。
I keep pencils and an eraser in my pencil case.
新しい筆箱を買ってもらった。
I got a new pencil case.
Similar meaning, but 筆入れ is less common and may specifically refer to a brush holder or case.
Compound of 筆 (fude, 'writing brush') and 箱 (hako, 'box'). The reading ふでばこ results from rendaku voicing of はこ to ばこ.