A connector unit comprising: a first connector having a first connector housing receiving a first terminal; and a second connector having a second connector housing receiving a second terminal, said first and second connectors (1, 2) being fitted to each other by facing each other and pressing in a fitting direction, wherein the second connector includes a spacer provided movably in between a temporary locking position where the second terminal is allowed to fall out of the second connector housing and a regular locking position where the second terminal is prevented from falling out of the second connector housing, wherein the first connector housing includes a fitting concave having an inner wall portion extended in the fitting direction and formed in substantially a circular shape, and the inner wall portion has a first step portion extended perpendicular to the fitting direction and projected inward, wherein the second connector housing includes a fitting convex having an outer wall portion extended in the fitting direction and formed in substantially a columnar shape, and the outer wall portion has a second step portion indented inward corresponding to the first step portion, and wherein the spacer has two outer walls (23B, 23C) projecting from at least two positions of a part of the outer wall portion and the second step portion of the fitting convex in the temporary locking position, and is sunken in the outer wall portion or arranged in the same plane as the outer wall portion in the regular locking position, characterized in that one of the first step portion of the fitting concave and the second step portion of the fitting convex is provided with a guiding groove extended in the fitting direction, and the other is provided with a projection to be inserted into the guiding groove, and in that in the temporary locking position, the projected first spacer outer wall is abutted on around a first inner wall of the fitting concave, and the second spacer outer wall is abutted on around a second sub inner wall of the fitting concave, thereby the fitting convex cannot be smoothly inserted and the middle insertion condition of the spacer can be detected. a first connector having a first connector housing receiving a first terminal; and a second connector having a second connector housing receiving a second terminal, said first and second connectors (1, 2) being fitted to each other by facing each other and pressing in a fitting direction, wherein the second connector includes a spacer provided movably in between a temporary locking position where the second terminal is allowed to fall out of the second connector housing and a regular locking position where the second terminal is prevented from falling out of the second connector housing, wherein the first connector housing includes a fitting concave having an inner wall portion extended in the fitting direction and formed in substantially a circular shape, and the inner wall portion has a first step portion extended perpendicular to the fitting direction and projected inward, wherein the second connector housing includes a fitting convex having an outer wall portion extended in the fitting direction and formed in substantially a columnar shape, and the outer wall portion has a second step portion indented inward corresponding to the first step portion, and wherein the spacer has two outer walls (23B, 23C) projecting from at least two positions of a part of the outer wall portion and the second step portion of the fitting convex in the temporary locking position, and is sunken in the outer wall portion or arranged in the same plane as the outer wall portion in the regular locking position, characterized in that one of the first step portion of the fitting concave and the second step portion of the fitting convex is provided with a guiding groove extended in the fitting direction, and the other is provided with a projection to be inserted into the guiding groove, and in that in the temporary locking position, the projected first spacer outer wall is abutted on around a first inner wall of the fitting concave, and the second spacer outer wall is abutted on around a second sub inner wall of the fitting concave, thereby the fitting convex cannot be smoothly inserted and the middle insertion condition of the spacer can be detected.