A terminal block comprising: a busbar component comprising: a busbar; a ring-shaped O-ring attached to a busbar main body of the busbar; and a holder attached to the busbar main body through an insertion hole of the holder, wherein the busbar main body is formed with a busbar-side engagement portion; the holder has a holder main body which is arranged between the busbar-side engagement portion and the O-ring and which has the insertion hole of the holder; the holder has a pair of terminal engagement portions which are continuous with left and right end portions of the holder main body; the holder main body is formed with, on one opening side of the insertion hole, a ring-shaped pressing portion which is pressed against the O-ring; and the holder main body is formed with, on another opening side of the insertion hole, a holder-side engagement portion which is engaged with the busbar-side engagement portion; the terminal block further comprising: a housing to which the busbar component is attached, wherein the housing has a busbar insertion hole through which the busbar main body of the busbar component is inserted, an O-ring housing portion which houses the O-ring of the busbar component, and a holder housing portion which houses the holder main body of the busbar component; wherein the busbar insertion hole, the O-ring housing portion, and the holder housing portion are formed so as to share the same axis that extends in a direction in which the busbar-side engagement portion is engaged with the holder-side engagement portion; wherein an outside terminal portion extends from one end of the busbar main body perpendicularly to the axial direction of the busbar main body, and wherein the holder main body is engaged with the outside terminal portion by a pair of engagement pieces, which are side portions of the outside terminal portion, being engaged with the pair of terminal engagement portions. a busbar; a ring-shaped O-ring attached to a busbar main body of the busbar; and a holder attached to the busbar main body through an insertion hole of the holder, wherein the busbar main body is formed with a busbar-side engagement portion; the holder has a holder main body which is arranged between the busbar-side engagement portion and the O-ring and which has the insertion hole of the holder; the holder has a pair of terminal engagement portions which are continuous with left and right end portions of the holder main body; the holder main body is formed with, on one opening side of the insertion hole, a ring-shaped pressing portion which is pressed against the O-ring; and the holder main body is formed with, on another opening side of the insertion hole, a holder-side engagement portion which is engaged with the busbar-side engagement portion; the terminal block further comprising: a housing to which the busbar component is attached, wherein the housing has a busbar insertion hole through which the busbar main body of the busbar component is inserted, an O-ring housing portion which houses the O-ring of the busbar component, and a holder housing portion which houses the holder main body of the busbar component; wherein the busbar insertion hole, the O-ring housing portion, and the holder housing portion are formed so as to share the same axis that extends in a direction in which the busbar-side engagement portion is engaged with the holder-side engagement portion; wherein an outside terminal portion extends from one end of the busbar main body perpendicularly to the axial direction of the busbar main body, and wherein the holder main body is engaged with the outside terminal portion by a pair of engagement pieces, which are side portions of the outside terminal portion, being engaged with the pair of terminal engagement portions. a housing to which the busbar component is attached, wherein the housing has a busbar insertion hole through which the busbar main body of the busbar component is inserted, an O-ring housing portion which houses the O-ring of the busbar component, and a holder housing portion which houses the holder main body of the busbar component; wherein the busbar insertion hole, the O-ring housing portion, and the holder housing portion are formed so as to share the same axis that extends in a direction in which the busbar-side engagement portion is engaged with the holder-side engagement portion; wherein an outside terminal portion extends from one end of the busbar main body perpendicularly to the axial direction of the busbar main body, and wherein the holder main body is engaged with the outside terminal portion by a pair of engagement pieces, which are side portions of the outside terminal portion, being engaged with the pair of terminal engagement portions.